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  #1  
Old 02-14-2012, 07:03 AM
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Default 39t sprocket

I have been reading alot online about the low and mid range gain on my 150 by going with a 39t sprocket and longer chain!
Can anyone that has done this mod confirm it !
Is it wort it ?
My buggies have a great top end speed but had flat spots in low and mid !
Thanks to Sycarms i adjusted the valves and got alot more out of the old girls but always looking for alittle more.
I ride on ruff flat trails here in Florida and lots of loose sand and saw Palmettos on the ground!
On another cart i have with tons of low end we find it easier to drift and power spin in the tight turns do to the sand !
Triing to get the crossfire 150,s to do the same!
Any help would be great
Thanks
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Old 02-15-2012, 11:16 AM
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It does help considerably, another option is to change the internal ratio. I believe there are 4 different sets of internal gearing combos. Sorry but it has been awhile, I'm sure Tom can fill you in more on this option.
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Old 02-15-2012, 03:00 PM
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thanks
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Old 02-17-2012, 09:45 AM
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yes the 39 tooth makes a difference, it changes the power band of the engine. the final drive gears make a difference also, most come with 13/43 gear set
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Old 02-17-2012, 12:05 PM
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Sand eat hp big time
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Old 02-17-2012, 05:36 PM
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I just got a 39 with a weld on hub from *************. Gonna weld it up this weekend.
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Old 02-18-2012, 10:37 PM
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I just put the 39T on my Spiderbox yesterday and it has much more power! I have tons of mods on it already, but I wanted the 39T so I can climb hills much easier and if I have a passenger I'd have no problems toting them around.

My engine is also geared very low (I think it's the lowest) 13/40 internal.. and 16/39 external. So it's not that fastest but on the trails it's hard to keep up with me.

I also have an Uni intake type, 125 jet, orange cdi, red coil, iridium spark plug, 10g rollers, yellow clutch springs and contra spring, Reverse, 22" mud tires on the back 19"s up front.

Lyon do you have a link to the weld on hub and sprocket? just curious to what it is.

Last edited by T3beatz; 02-19-2012 at 07:56 PM.
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Old 02-19-2012, 07:02 AM
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looks like im going to spring for it then , I know im going to have to either lengthen my chain by 4 links or just buy new ones, Grrrrr just bought chains for both buggies
Yes would love to see the wilded one . I Also have some play in the rear hubs of one of my crossfires ! How much play should thier be ?
I have weled everthing on it now so i noticed a new sound i have not herd before and track it to the rear hubs 1/4 inch slop at the hubs.
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Old 02-19-2012, 07:15 AM
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Quote:
Originally Posted by T3beatz View Post
My engine is also geared very low (I think it's the lowest) 13/40 internal.. and 16/39 external. So it's not that fastest but on the trails it's hard to keep up with me.
How did you ck this ? I'm curious on what mine is

Quote:
Originally Posted by T3beatz View Post

I also have an Uni intake, 25 jet, orange cdi, red coil, iridium spark plug, 10g rollers, yellow clutch springs and contra spring, Reverse, 22" mud tires on the back 19"s up front.
did you mean 125 jet? this one threw me for a loop.
which one of these do you think made the *most* difference right away ?
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Old 02-19-2012, 09:33 AM
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My Howhit on the Yerf is a 13/40 gear combination. Only way to know FOR SURE is to remove the final drive cover and count the teeth.

Or if you can find any info from the manufacturer... Say maybe in a repair manual? (and that's only if a previous owner didn't change them out)
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Old 02-19-2012, 10:46 AM
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I know you asked T3, but I've kept pretty good records of my performance gains after each modification to my Yerfdog 3206.

Stock Spiderbox configuration: 13/40 internal gears, 13T engine sprocket, 31T axle sprocket, and 743 20 30 Gates belt.

All measurements were taken with a Garmin Etrex handheld GPS, on concrete, with a set distance (approx 300'), on the same "track".

22.3 MPH as is from previous owner (stock tires, slightly deflated, stiff front suspension)

23.1 MPH performance coil, performance CDI (both orange from Ebay), no air filter and 125 main jet

23.7 MPH opened muffler opening (1/2" stock VS. 3/4")

24.9 MPH home ported head and port match intake manifold

26.3 MPH MAX SPEED (first run on street)

25.2 MPH 10g Dr. Pulley sliders with cleaned/lubed CVT, and deglaze clutch and bell

29.8 MPH MAX SPEED

26.8 MPH New tires and bearings (22" rear), FMF slip on exhaust, UNI air filter with 6" extension

33.2 MPH MAX SPEED

27.2 MPH 8" extension for air filter

33.0 MPH MAX SPEED

28.0 MPH NCY CDI (orange with aluminum housing)

33.0 MPH MAX SPEED

All readings were taken with all upgrades added to one another. Only the air filter extension was substituted.

Round 2 Test and tune


28.6 MPH 12 gram Dr. Pulley sliders and header wrap for 7"

35.3 MPH MAX

30.1 MPH A11 cam installed (needs larger pilot jet)

38.9 MPX MAX


Last test and tune session with basic "stock" engine:

29.6 MPH with stock rollers
37 MPH MAX

30.2 MPH with Dr. Pulley variator and 12g sliders
38.3 MPH MAX

I tried getting readings with a 6", 7", and 8" red neck tube extension, but they were all around the same speeds in accel. I didn't have the jetting nailed down yet with the A11 cam until after I made the passes. The kart was blubbering off the line.

Ended up using 35 pilot, 2 1/2 turns on the mixture screw, and a 122.5 main jet for good reults.

So no improvement from the last test session. 12g sliders in the stock variator seemed to work best for me.

OK, so now I have the 62mm BBK kit installed

32.7 MPH in 300'

Max speed 40.2 MPH


Time to install the good stuff......

Last edited by xlint89; 11-09-2014 at 10:18 PM.
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Old 02-19-2012, 05:10 PM
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xlint89 - cool, glad you did these measurements... any gut feel for the best for the most upgrade ? jets for example? I know each upgrade tends to need another (more gas needs more exhaust). I did the air filter and jet, and did feel and hear a difference, but never measured.
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Old 02-19-2012, 07:12 PM
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Great info
I'm curious--How much did you spend to get 10 more MPH?
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Old 02-19-2012, 07:15 PM
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Quote:
Originally Posted by satoys View Post
How did you ck this ? I'm curious on what mine is


did you mean 125 jet? this one threw me for a loop.
which one of these do you think made the *most* difference right away ?
Sorry, yeah I meant the 125 jet. the most difference to me was the re-jet, air intake, and CDI, I was able to pick up a few extra MPH and more power for hills.

Oh, and I checked my gear count when I had the engine broken down to change out the output shaft, to mount the reverse, I have the Howhit GY6.

I need to test my speed, but I've put about $120.00 bucks into the engine so far for upgrades.

All purchased from ebay
Orang CDI $15.00
Foam Air intake 9.99
intake oil 9.99
Jet set 11.05 shipped (115,120,125,130,135)
coil/boot 13.68
iridium spark plug 9.99
10g rollers 9.99
1500 contra spring 11.00
1500 clutch springs 9.95


a different place
39T sprocket 21.95 http://www.highrpmracer.com/rear-spr...0-p-11553.html
38 pilot jet 4.95 http://www.scrappydogscooters.com/12...OKE_PARTS.html

All these upgrades helped tons on my trails I can tell the difference big time on the big hills. Before when I would climb them I could notice the buggy bogging down toward the top a little, and the pedal would have to be floored, but now it spins the tires if I give it full throttle on the same hills, and I don't have to have speed to climb them. Since I've moved to the 39T sprocket I'm going install a set of 12g or 13g sliders to get my speed back. I'm also going to be getting a Performance Muffler soon, maybe one of the 90 dollar ones from ebay, I know that is probably the most restrictive part in my setup now.
http://www.ebay.com/itm/Silver-scoot...ht_1901wt_1133

T.J.

Last edited by T3beatz; 02-19-2012 at 08:06 PM.
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Old 02-19-2012, 07:53 PM
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thanks T3 ! and especially thanks for the links...
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Old 02-19-2012, 10:18 PM
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Quote:
Originally Posted by satoys View Post
xlint89 - cool, glad you did these measurements... any gut feel for the best for the most upgrade ? jets for example? I know each upgrade tends to need another (more gas needs more exhaust). I did the air filter and jet, and did feel and hear a difference, but never measured.
Honestly, I can't pinpoint 1 specific mod. A cluster of them will open your eyes to a more powerful engine though.

UNI filter $20

PVC extension $4

rejet carb FREE (I have a ton of jets available from working on my skis)

Performance coil $15

Performance CDI $20 NCY CDI (preferred) $35

FMF slip on muffler (used on Ebay $30 shipped)

Home ported head with port matching FREE

Dr. Pulley 10g sliders $25

Clean/lube CVT FREE

Deglaze clutch and bell FREE

Total = $ 130

Total performance gained = 3+ MPH in 300'

This is what you can REALLY feel. Takes off much better, I'm sure I'll be able to climb any hills much easier too.

Last edited by xlint89; 02-19-2012 at 11:06 PM.
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Old 02-19-2012, 10:45 PM
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Quote:
Originally Posted by xlint89 View Post
I know you asked T3, but I've kept pretty good records of my performance gains after each modification to my Yerfdog 3206.

Stock Spiderbox configuration: 13/40 internal gears, 13T engine sprocket, 31T axle sprocket, and 743 20 30 Gates belt.

All measurements were taken with a Garmin Etrex handheld GPS, on concrete, with a set distance (approx 300'), on the same "track".

22.3 MPH as is from previous owner (stock tires, slightly deflated, stiff front suspension)

23.1 MPH New 24mm carb $26, performance coil $15, performance CDI $20, (both orange from Ebay) no air filter and 125 main jet FREE

23.7 MPH opened muffler opening (1/2" stock VS. 3/4") FREE

24.9 MPH home ported head and port match intake manifold FREE

26.3 MPH MAX SPEED (first run on street)

25.2 MPH 10g Dr. Pulley sliders $25 with cleaned/lubed CVT, and deglaze clutch and bell FREE

29.8 MPH MAX SPEED

26.8 MPH New tires and bearings (22" rear) $300, FMF slip on exhaust $30, UNI air filter $20, with 6" extension $4

33.2 MPH MAX SPEED

27.2 MPH 8" extension for air filter (cut from same piece as 6")

33.0 MPH MAX SPEED

28.0 MPH NCY CDI (orange with aluminum housing) $35

33.0 MPH

All readings were taken with all upgrades added to one another. Only the air filter extension was substituted.
Quote:
Originally Posted by metalstudman1 View Post
Great info
I'm curious--How much did you spend to get 10 more MPH?
Oh boy..... I hope the GF doesn't see this thread!!!

Please understand that the first posted speed was in rough shape, and NOT max speed. So technically, I didn't gain 10 MPH. I never did a MAX speed baseline run "as is".

Total $475 plus some shipping costs as well

But, as you can see, it's greatly improved the performance, the ride, and the fun factor. So it was well worth it.

However, I am not done yet. I am looking to gain more top speed still.

What I have left to test though:

Dr. Pulley variator

12g sliders

I would also like to try the Kidnme performance clutch pulley, bigger belt, and Dr. P variator and see what that gets me.

This is all done with the stock 150cc engine.

I've got other plans once testing is over.
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Old 02-20-2012, 01:36 AM
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As far as speed goes the 10g sliders or rollers are going to limit your speed a tad (not heavy enough to push the variator all the way out, especially if you have higher rated contra springs installed), but give you good low end power.

If your going strictly for speed then simple other mods will get you there.

The Dr. pulley variator looks good but I would like to try the DR 2 performance variator (but that fact that it does not have a fan is weird to me).

I'm gonna test my speed next time I go out. My goal is about 25-30mph, but will get there pretty fast, and have great power for trails.

Last edited by T3beatz; 02-20-2012 at 01:44 AM.
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Old 02-20-2012, 06:27 AM
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This is all great info for anyone moding a gy6 120 , I thank you all very much.
The trails i ride here in florida have no real hills to speak of yet ! I need to barrow a dozer for the weekend. I am on sandy tails with lots of saw palmettos , "small palm trees " anout 2 to 3 feet tall ! I had a farmer use his disc cutter on some of it to clear the saw palmettos out ! So at the end of the day i need good low end grunt to turn out of the corners , My back trails only have 2 or three spots that i can hit the rev limiter. So the next upgrades will be a 39t and a nyc cdi no rev limit. the stock buggies would not break 20 mph. Keeping in mind i got them used and with no upgrades at all.
What ive done so far.
130 jet
orange coil
dr pulley clutch
dr pulley teflon vibrator with 10g rollers
1500 rpm yellow spring
uni ait filter
polished intake manifold
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Old 02-20-2012, 07:02 AM
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Oh boy..... I hope the GF doesn't see this thread!!!
Total $475 plus some shipping costs as well


think like a politician, it's all how you spin it...

"Look honey, I was not wasting money hanging out at bars, chasing women.... I was here at home with you, building something you can enjoy with me"
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Old 02-20-2012, 11:59 AM
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Quote:
Originally Posted by satoys View Post
Oh boy..... I hope the GF doesn't see this thread!!!
Total $475 plus some shipping costs as well


think like a politician, it's all how you spin it...

"Look honey, I was not wasting money hanging out at bars, chasing women.... I was here at home with you, building something you can enjoy with me"
But what if he was at the bars too? lol

drillpvt, seems you have done a few good upgrades already, and if I'm not mistaken I think the crossfire has the howhit gy6 engine also so it should have the low internal gearing (13/40).

the 39T sprocket should get you a little more low end grunt and should help move the crossfire around in that sand a little better. Next I would mod the current muffler or buy a performance one for a little more HP.
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Old 02-20-2012, 02:25 PM
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I have moded the stock pipe , Sorry i should have posted that . It is a howit gy6 , next is the 39t sprocket , then Cam upgrade then carb. alot of people have told me the 30 to 32 mil pumper carbs wont do to much with out a better Cam . Never done a cam before so it will be intresting ! but im only doning that on one of the Crossfires ! I am looking for a good used 250cc on craiglist and online to throw into the other one.
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Old 02-20-2012, 02:59 PM
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Quote:
Originally Posted by drillpvt View Post
I have moded the stock pipe , Sorry i should have posted that . It is a howit gy6 , next is the 39t sprocket , then Cam upgrade then carb. alot of people have told me the 30 to 32 mil pumper carbs wont do to much with out a better Cam . Never done a cam before so it will be intresting ! but im only doning that on one of the Crossfires ! I am looking for a good used 250cc on craiglist and online to throw into the other one.
If I was to go up to the 30/32mm carb I'd go with a 63mm big bore kit, or a stroker crank. The extra fuel/air will be needed for the extra displacement on the stock gy6's the stock carb should be fine with just a re-jet... the cost vs performance gain with just changing the carb out probably wont be that significant without adding more space in the engine for combustion.

The big bore kit's can be found for as low as 80-90 bucks, but you will have to have the crank case machined for any big bore kit over 59mm

The 59mm big bore kit will take you up to about 158cc's over the stock 149 (or 148 in the howhits).

63mm will get you about 180cc's. (I'm sure you may know all of this, but someone who may be looking over this thread may want to know).

just found this... http://www.**********.com/buggy-tech...ore-stroker/16

big bore kit 59mm... http://www.ebay.com/itm/157QMJ-GY6-p...#ht_912wt_1396

Last edited by T3beatz; 02-20-2012 at 03:15 PM. Reason: link
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Old 02-20-2012, 03:44 PM
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this is what happens when you buy a bigger intake for the crossfire gy6 buggies. The intake is about 3/4 of a inch longer were the carb goes on ! the carb no longer fits into the engine cage the right way , it also hits the top engine mont ! grrrrrr, I paid a whopping 22.00 dollars for this thing so being the redneck i am it was going on it one way or another lol .
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Old 02-20-2012, 04:29 PM
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So that's what a spare Spiderbox A-arm get's used for!!!!!
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Old 02-20-2012, 05:02 PM
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Nope lol it came off my sons buggy , Used to be part of his gas tank rack on the back !
Im making him a new tank anyway !
Do what you can with what ya got !
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Old 02-20-2012, 06:12 PM
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this is what happens when you buy a bigger intake for the crossfire gy6 buggies. The intake is about 3/4 of a inch longer were the carb goes on ! the carb no longer fits into the engine cage the right way , it also hits the top engine mont ! grrrrrr, I paid a whopping 22.00 dollars for this thing so being the redneck i am it was going on it one way or another lol .
I used a piece of "air snorkel" hose that came with the carter to extend under the cross bar. -- I think it wasn't anything more than hose from a vacuum cleaner or pool filter. Fit really nice and snug around the carb and the filter adapter. I think i've read somewhere that 6 to 8 inches is the max length for extending the air filter from the carb. Anyone have insight on this? I'd actually like to be able to get the filter up around or above the rack just to keep it out of the mud zone.
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Old 02-20-2012, 06:19 PM
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The connector that came with my uni filter is only 3 inches but the whole problem was the cross bar was in the way , when i put on the polished intake manifold going into the motor , It was the new part that was taller and longer then the stock . Airfilter use to fit nicely under the cross bar . now its dead in line with it. Hence the cutting and butcher job welding.
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Old 02-20-2012, 07:16 PM
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@ drillpvt, got to do what ya got to do some times, as long as it works.

I just went out and did a few speed tests with my Yerf with the 39T sprocket. The first couple runs were ok, but something was wrong on the top end, I was getting horrible popping and it felt as if I was stepping on the breaks slightly, Top speed was 26mph. I went back into the garage and checked my plug and it was on the white side (lean). So I took out my stash of jets and removed the 125 that was in and replaced it with a 130. Went back out for a few more runs and the engine sounded much better still a slight popping once I got to the very peak of speed but I was able to hit 30mph with no problems. I think I'm going to have to move to a 132.5 jet for now, This is puzzling because I still have the stock muffler on it, I didn't think I would need such a high jet size. My friends have told me that My muffler sounds different from theirs, it has a beefier sound (we all have howhit gy6's with the stock mufflers).

So all in all with the 39T sprocket you can still get decent top speeds with a lot of low end power. Going to the 12G sliders will probably get me 2-3 more mph.
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Old 02-21-2012, 12:38 AM
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Quote:
Originally Posted by T3beatz View Post
As far as speed goes the 10g sliders or rollers are going to limit your speed a tad (not heavy enough to push the variator all the way out, especially if you have higher rated contra springs installed), but give you good low end power.

If your going strictly for speed then simple other mods will get you there.

The Dr. pulley variator looks good but I would like to try the DR 2 performance variator (but that fact that it does not have a fan is weird to me).

I'm gonna test my speed next time I go out. My goal is about 25-30mph, but will get there pretty fast, and have great power for trails.
Yeah, we'll see what the 12g sliders does for my top speed, and how it affects the 300' test.

Stock contra spring is in it. I'm thinking of trying the ball bearing spring base though.

http://www.sycpowersports.com/index....id=66&incid=29

Supposed to prevent the spring from binding = smoother transitions

And it will actually stiffen the stock spring 15% I read due to the raised height of the base because of the bearings and double "seat" if you will...
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Old 02-21-2012, 12:40 AM
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Quote:
Originally Posted by satoys View Post
Oh boy..... I hope the GF doesn't see this thread!!!
Total $475 plus some shipping costs as well


think like a politician, it's all how you spin it...

"Look honey, I was not wasting money hanging out at bars, chasing women.... I was here at home with you, building something you can enjoy with me"
You must be a lawyer.......
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Old 02-21-2012, 12:47 AM
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Originally Posted by x-bird View Post
I used a piece of "air snorkel" hose that came with the carter to extend under the cross bar. -- I think it wasn't anything more than hose from a vacuum cleaner or pool filter. Fit really nice and snug around the carb and the filter adapter. I think i've read somewhere that 6 to 8 inches is the max length for extending the air filter from the carb. Anyone have insight on this? I'd actually like to be able to get the filter up around or above the rack just to keep it out of the mud zone.
I have read that before. The explanation was that jetting the carb was to be difficult/irratic when using an extension longer than 6".

I kind of find that to be odd since the stock intake length on my Yerf was 8"...

But, as you can see the 8" extension yielded almost 1/2 MPH gain over the 6" in the 300' test, and only lost .2 MPH on MAX speed.

That's the best I could come up with
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Old 02-21-2012, 01:09 AM
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Originally Posted by T3beatz View Post
If I was to go up to the 30/32mm carb I'd go with a 63mm big bore kit, or a stroker crank. The extra fuel/air will be needed for the extra displacement on the stock gy6's the stock carb should be fine with just a re-jet... the cost vs performance gain with just changing the carb out probably wont be that significant without adding more space in the engine for combustion.

The big bore kit's can be found for as low as 80-90 bucks, but you will have to have the crank case machined for any big bore kit over 59mm

The 59mm big bore kit will take you up to about 158cc's over the stock 149 (or 148 in the howhits).

63mm will get you about 180cc's. (I'm sure you may know all of this, but someone who may be looking over this thread may want to know).

just found this... http://www.**********.com/buggy-tech...ore-stroker/16

big bore kit 59mm... http://www.ebay.com/itm/157QMJ-GY6-p...#ht_912wt_1396
You might have to look before you purchase parts first.

Post #20 shows a Howhit bore

http://buggymasters.com/forum/showthread.php?t=2665

I think the only viable option for guys with this motor are the 58.5mm/59mm bbk and a stroker crank.

Plus I've read the 63mm kit gets to be pretty thin on the cyl walls. Not good from a structuarl stand point.

I think most prefer the 62mm kit with slightly thicker cyl walls for longevity.

Last edited by xlint89; 02-21-2012 at 01:13 AM.
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Old 02-21-2012, 01:32 AM
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I personally wouldn't go past the 59mm (seems easy enough to install), the stroker crank looks appealing but $200 bucks and a ton of work later doesn't! lol. I'm sure the 59mm will be plenty of power for me. Right now as is I'm sure it has enough power to get through most of the trails we have around here, and may even keep up with some 250's!

I'ts a 150, I'll try and get as much power out of it as I can without going overboard on spending. I don't want to put 1000 bucks into this buggy, knowing I can find a decent 250 for $1200-$1500.

@xlint89 I think that's about right, you can still get it bored to a certain point.

here is a vid you can see how thin the walls are and they guy still has to bore it out for the 63mm jug. The inner diameter is 63mm, the walls are thinner so you don't have to bore out as much on the crankcase.

http://www.youtube.com/watch?v=R1GFv...eature=channel

Last edited by T3beatz; 02-21-2012 at 01:52 AM.
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Old 02-21-2012, 02:30 PM
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If you have to split the case for any reason or replace a stock crank shaft, the stroker crank should be on your parts list. It will provide more torque (which is what any 150 needs). You'll have to decide if it's worth your time splitting open a good engine to install a crank.
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Old 02-21-2012, 04:46 PM
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Quote:
Originally Posted by GX150 View Post
If you have to split the case for any reason or replace a stock crank shaft, the stroker crank should be on your parts list. It will provide more torque (which is what any 150 needs). You'll have to decide if it's worth your time splitting open a good engine to install a crank.
This is exactly what I'm thinking.

It's been recommended to me to change out the stock starter clutch if you're going to be adding more power/compression to the engine.

If you're going that far in, might as well go a little bit more. Ceramic/Nikasil 59mm with a 2.2mm stroker crank should be nice.
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Old 03-07-2012, 10:56 PM
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Quote:
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xlint89 - cool, glad you did these measurements... any gut feel for the best for the most upgrade ? jets for example? I know each upgrade tends to need another (more gas needs more exhaust). I did the air filter and jet, and did feel and hear a difference, but never measured.
More new mods and speeds affected by them have been added to my first post.


My new best mod thus far has got to be the A11 camshaft.

NOTE: that other mods must be in place to reap full benefit of the larger cam. Like ign, air filter, exhaust, etc....
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Old 03-07-2012, 10:58 PM
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what do you feel with the A11 over the stock?
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Old 03-07-2012, 10:59 PM
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Quote:
Originally Posted by xlint89 View Post
I know you asked T3, but I've kept pretty good records of my performance gains after each modification to my Yerfdog 3206.

Stock Spiderbox configuration: 13/40 internal gears, 13T engine sprocket, 31T axle sprocket, and 743 20 30 Gates belt.

All measurements were taken with a Garmin Etrex handheld GPS, on concrete, with a set distance (approx 300'), on the same "track".

22.3 MPH as is from previous owner (stock tires, slightly deflated, stiff front suspension)

23.1 MPH performance coil, performance CDI (both orange from Ebay), no air filter and 125 main jet

23.7 MPH opened muffler opening (1/2" stock VS. 3/4")

24.9 MPH home ported head and port match intake manifold

26.3 MPH MAX SPEED (first run on street)

25.2 MPH 10g Dr. Pulley sliders with cleaned/lubed CVT, and deglaze clutch and bell

29.8 MPH MAX SPEED

26.8 MPH New tires and bearings (22" rear), FMF slip on exhaust, UNI air filter with 6" extension

33.2 MPH MAX SPEED

27.2 MPH 8" extension for air filter

33.0 MPH MAX SPEED

28.0 MPH NCY CDI (orange with aluminum housing)

33.0 MPH MAX SPEED

All readings were taken with all upgrades added to one another. Only the air filter extension was substituted.

Round 2 Test and tune


28.6 MPH 12 gram Dr. Pulley sliders and header wrap for 7"

35.3 MPH MAX

30.1 MPH A11 cam installed (needs larger pilot jet)

38.9 MPH MAX
Bump


Last edited by xlint89; 03-07-2012 at 11:04 PM.
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Old 03-07-2012, 11:03 PM
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Quote:
Originally Posted by T3beatz View Post
what do you feel with the A11 over the stock?
Alot more oomph!!!!


Stock cam with 12g sliders was 28.6 MPH in 300' and 35.3 MPH top speed. (not bad)

With A 11 cam (didn't touch jetting yet) got 30.1 MPH in 300' and 38.9 MPH MAX speed. (awesome...)

That's 1.5 MPH in 300' gain and 3.5 MPH on top end just from the cam alone. And that's on top of all the other mods I've done.


Guys, keep in mind, this is still with the stock variator, clutch, 24mm carb, and stock intake manifold.

Last edited by xlint89; 03-07-2012 at 11:14 PM.
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Old 03-07-2012, 11:13 PM
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And if you look, just from today's swap (12g sliders and A11 cam) I gained 2.1 MPH in the 300' test and 5.9 MPH in top speed VS. my last personal best.

I honestly feel if I would have ran her for a touch longer on the straight away, she'd might have gone a little faster.
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Old 03-07-2012, 11:22 PM
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Oh cool stuff, Grab that 39T sprocket and see that top speed drop!
my max speed now is 30.1mph takin with my vapor, my max RPM was 9340rpms. I still have the stock muffler, and 10gram rollers, that probably is my limiting factor right now, but it's not loud and it doesn't sound to bad. I'm gonna get the sliders very soon, I just don't feel like taking my CVT cover off again. lol
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Old 03-08-2012, 12:06 AM
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If you still are running that 13t engine with the 39t axle 30 mph is max red line. With the 16t reverse sprocket , I would expect mid 30's if you go to a 115mm variator and 12g sliders.
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Old 03-08-2012, 12:23 AM
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I have the 16T reverse sprocket on mine, and the stock variator. I'm sure I could pick up some speed with heavier rollers/sliders, that's why I'm going to grab a set of 12grams I should be able to gain a couple mph with that.
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Old 03-08-2012, 12:39 AM
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Remember that changing variator weights does not change your gearing only your shift rate. 12g sliders have the equivalent response of 10g rollers but allow the variator greater range due to their shape.
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Old 03-08-2012, 12:42 AM
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yeah, going with the 12g sliders should keep me on par with my 10g rollers on the low end, but give me a little more speed up top (not that I need it on the trails).

but in a way changing the weights does change your gearing... If you have really light weights, like 8g ones the belt probably wont get close to the top of the variator, limiting your gearing. Now if you stick some 15g ones in the belt will ride up much higher on the variator increasing your gearing. But, you also have to factor in the Contra spring too, if you have the light weights in and 2000rpm contra springs you'll be rollin slow but with good power because of the "belt gearing" on the CVT, because the weights are so light they can't push the spring fully apart pulling the belt down on the clutch side. Run those same light weights with a 1000rpm contra spring and you'll get more speed and faster shift... Basically it all gets factored in, so in an essence it does change the gearing.
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Last edited by T3beatz; 03-08-2012 at 01:48 AM.
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Old 03-09-2012, 12:28 AM
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The crossfire uses the 13/40 final gears which figures 3:08. They now make a 11/43 but the case has to be cut a bit for the 43 tooth gear to fit(no big deal). Just installed it but haven't tried it yet.

TOM
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Old 03-09-2012, 01:04 AM
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11/43, now that has to be slow! 13/40 averages around 30ish from reading around, so 11/43 has to be 25 or so.
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Old 03-09-2012, 01:26 AM
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I'm getting to the 300' mark going 43mph at 8400 rpm, but my engine is still pulling @ 9200 rpm so I figure the 3:90 ratio will get my rpm's up faster thus getting me there faster and in less time. But I'm sure I will also have to add weight to the cvt as well. My buggy will top out about 52 mph. I'm working in the 300' range since what I want is the quickest burst I gan get. Most trails have bumps and curves and on average speed ranges around 25 to 30mph and that is pushing it. But when you get to a strait the atv's will pull away from the buggy. This will give me more power to keep up with the atv's, plus I like to drag race and every bit helps.
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Old 03-09-2012, 09:20 AM
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I meant to ask what was your external gear ratio? 13/31? or 16/39?

because I have the 13/40 internal with the 16/39 external, and 30 is my max. so if your gearing is longer than that that would explain that 43mph in the 300'.

T.J.
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Old 03-09-2012, 09:45 AM
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Right now I am running the 16/34, but will also test it with the 16/39.Technically since I run the 24' rear tire they come to 16/32 and 16/37.


TOM
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Old 03-09-2012, 10:00 AM
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24' rear tire or 24" lol we know what you mean. That extra 2" on the rear tire makes a difference also, that should give you a little boost in speed so that extra torque would be handy to spin the bigger tires. I'd guess most of us are running 22s on the back.
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Old 03-09-2012, 10:07 AM
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:Yea I guess 24' tires would be pushing it just a bit
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Old 03-10-2012, 06:52 AM
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Quote:
Originally Posted by x-bird View Post
I think i've read somewhere that 6 to 8 inches is the max length for extending the air filter from the carb. Anyone have insight on this? I'd actually like to be able to get the filter up around or above the rack just to keep it out of the mud zone.
If you go by the math, CC's ,displacment, stroke and all that other techno stuff it works out to be a total of 14" measured from the end of the velocity tube, through the carb, intake , head tract to the combustion side of the intake valve. Taking into account the thickness of gaskets and couplers. I measured this a while back and came up with a velocity tube of approx. 6.75 ". There's too many variables to nail it down but something in that range works good.
The purpose of the tube is to reduce air turbulance and enhance velocity by straightening out the air flow before it enters the carb. Too long a tube reduces velocity. Too short doesn't give the air enough time to organize. Bends in the tube counter-act the purpose. Playing with the length does give a marked difference in throttle response and final air/fuel ratio.
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Old 03-10-2012, 07:29 AM
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Thanks ckau, that helps a lot. right now i'm finding that a straight shot out the carb and under the cross member of about 6 inches is putting the air filter right into the rear rack bar when the swingarm compresses about 3/4 of the way into it's travel.
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Old 03-10-2012, 09:35 AM
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I have read that anything longer than 6" begins to give jetting issues? However, the Yerf Dog has an intake tube of 8" before the air filter if I remember correctly.

In my experiment, I gained slighty better acceleration with the 8" tube over the 6", but lost .2 MPH on the top with it.

Maybe I should try a 7" just for kicks, and do a back to back to back test of them. Hmmm.....
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Old 03-10-2012, 11:57 PM
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Quote:
Originally Posted by xlint89 View Post
I know you asked T3, but I've kept pretty good records of my performance gains after each modification to my Yerfdog 3206.

Stock Spiderbox configuration: 13/40 internal gears, 13T engine sprocket, 31T axle sprocket, and 743 20 30 Gates belt.

All measurements were taken with a Garmin Etrex handheld GPS, on concrete, with a set distance (approx 300'), on the same "track".

22.3 MPH as is from previous owner (stock tires, slightly deflated, stiff front suspension)

23.1 MPH performance coil, performance CDI (both orange from Ebay), no air filter and 125 main jet

23.7 MPH opened muffler opening (1/2" stock VS. 3/4")

24.9 MPH home ported head and port match intake manifold

26.3 MPH MAX SPEED (first run on street)

25.2 MPH 10g Dr. Pulley sliders with cleaned/lubed CVT, and deglaze clutch and bell

29.8 MPH MAX SPEED

26.8 MPH New tires and bearings (22" rear), FMF slip on exhaust, UNI air filter with 6" extension

33.2 MPH MAX SPEED

27.2 MPH 8" extension for air filter

33.0 MPH MAX SPEED

28.0 MPH NCY CDI (orange with aluminum housing)

33.0 MPH MAX SPEED

All readings were taken with all upgrades added to one another. Only the air filter extension was substituted.

Round 2 Test and tune


28.6 MPH 12 gram Dr. Pulley sliders and header wrap for 7"

35.3 MPH MAX

30.1 MPH A11 cam installed (needs larger pilot jet)

38.9 MPX MAX


Last test and tune session with basic "stock" engine:

29.6 MPH with stock rollers
37 MPH MAX

30.2 MPH with Dr. Pulley variator and 12g sliders
38.3 MPH MAX

I tried getting readings with a 6", 7", and 8" red neck tube extension, but they were all around the same speeds in accel. I didn't have the jetting nailed down yet with the A11 cam until after I made the passes. The kart was blubbering off the line.

Ended up using 35 pilot, 2 1/2 turns on the mixture screw, and a 122.5 main jet for good reults.

So no improvement from the last test session. 12g sliders in the stock variator seemed to work best for me.


Time to install the good stuff......
It appears I have reached my limit with the engine in it's basic stock configuration.

My last test session has been added above.
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Old 03-11-2012, 08:14 PM
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what's next on the agenda to install? what are you going for speed are power?
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Old 03-11-2012, 09:47 PM
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Installed a NCY ceramic/Nikasil coated 155cc (58.5mm) BBK today.

I REALLY wanted a stroker crank, but decided against it. (I don't ride it enough to justify it. And I'm really quite impressed with the performance gains from the few "add ons")

I also installed a matching NCY ported head with ceramic coated exhaust port and valve faces.

Got a matching 30mm aluminum intake manifold.

I'm going to run a Keihin PE 28mm carb (round slide)

Finally, I want to experiment with a different exhaust as well.

Maybe try a 1" header same length as the stock pipe with the FMF slip on. (stock has 3/4" stepped up to a 1") You know, something similar to the HH exhaust.

I'd love to try a tuned length exhaust though. But I can't stomach the price for the TK.

Not too sure how good the MRP exhaust is???

Personally I want speed, but eventually, it'll shift to acceleration once I get on the trails. Right now it's just been blacktop and experimentation with parts.
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Old 03-15-2012, 02:52 PM
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sweet lets us know about the power and speed you get !
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Old 03-16-2012, 08:02 PM
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the mrp exhaust you will have to do some mods to get it to fit, the hh one fits with out the mods
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Old 03-18-2012, 03:23 AM
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MRP=JUNK plain and simple.
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Old 03-18-2012, 07:50 AM
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MRP=JUNK plain and simple.
lol
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Old 03-18-2012, 09:30 AM
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[QUOTE=EJ Mac;22297]MRP=JUNK plain and simple.[/QUOTE

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Old 03-18-2012, 10:50 AM
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M ost
R egretted
P urchase
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Old 03-21-2012, 10:20 AM
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Quote:
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M ost
R egretted
P urchase
Quote:
Originally Posted by ckau View Post
If you go by the math, CC's ,displacment, stroke and all that other techno stuff it works out to be a total of 14" measured from the end of the velocity tube, through the carb, intake , head tract to the combustion side of the intake valve. Taking into account the thickness of gaskets and couplers. I measured this a while back and came up with a velocity tube of approx. 6.75 ". There's too many variables to nail it down but something in that range works good.
The purpose of the tube is to reduce air turbulance and enhance velocity by straightening out the air flow before it enters the carb. Too long a tube reduces velocity. Too short doesn't give the air enough time to organize. Bends in the tube counter-act the purpose. Playing with the length does give a marked difference in throttle response and final air/fuel ratio.
The length of the cold air tube comparing 6" to 8" will be so small to worry about.Now when talking 4,6,or 8 cyl engines the science becomes critical when going for the most effficient performance. The important thing on the single cyl. engine or even the 2,or 3 cylinder engine which move the pistons without any variation, in other words up and down at the same time is to rid the intake path of any restrictions. The stock air box restricts due to its long bendy tubes leading into a large air box then restricting back down into a smaller tube actually interupts slowing down the air flow. When converting to a strait cold air intake all restrictions found in the stock airbox are removed. It really won't make any difference if the CAI is 6" or 12" unless you are to be in some competition where 100th of a second can mean the difference between winning and loosing. I run mine @ 10" total including filter so that I get the coolest air possible which will make a bigger difference. As far as the mud concern on the filter you just have to run a quality pre filter. There really nice for you just remove and run under water to clean, shake the water off and reinstall. This will take 30 seconds to do, well maybe a bit more but you get my point. Sand and mud will clog an oiled filter really fast so the prefilter is a necessity in those conditions.

As far as the exhaust goes, the MRP will be a great improvement over the stock exhaust but the price for not being a true tunned exhaust is its problem. But so is the Hammerhead exhaust. I will say this, I have tried the hammerhead exhaust on my 150 and actually lost power as compared to the MRP exhaust, probably due to the scavenging effect lost dur to a much less restriction, but my engine is not the average GY6. I can also say that one of my customers had the HH exhaust with my head and cam on his 250 cc and noticed a huge difference (his words) when installing the TK exhaust. The problem with the buggy world with perf. parts is they were either designed for the scooter or a non exact copy of something once designed for our buggies. The MRP exhaust was to be a cheaper alternative to the Eastside Exhaust of past but is not an exact copy so some of the low end torque gains the Eastside gave were lost in the MRP copy.
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Old 12-25-2012, 10:26 AM
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Installed a NCY ceramic/Nikasil coated 155cc (58.5mm) BBK today.

I REALLY wanted a stroker crank, but decided against it. (I don't ride it enough to justify it. And I'm really quite impressed with the performance gains from the few "add ons")

I also installed a matching NCY ported head with ceramic coated exhaust port and valve faces.

Got a matching 30mm aluminum intake manifold.

I'm going to run a Keihin PE 28mm carb (round slide)

Finally, I want to experiment with a different exhaust as well.

Maybe try a 1" header same length as the stock pipe with the FMF slip on. (stock has 3/4" stepped up to a 1") You know, something similar to the HH exhaust.

I'd love to try a tuned length exhaust though. But I can't stomach the price for the TK.

Not too sure how good the MRP exhaust is???

Personally I want speed, but eventually, it'll shift to acceleration once I get on the trails. Right now it's just been blacktop and experimentation with parts.
I'm curious to know your impression of the 58.5mm bore. This is one ive been looking at.
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Old 12-25-2012, 10:36 AM
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I have moded the stock pipe , Sorry i should have posted that . It is a howit gy6 , next is the 39t sprocket , then Cam upgrade then carb. alot of people have told me the 30 to 32 mil pumper carbs wont do to much with out a better Cam . Never done a cam before so it will be intresting ! but im only doning that on one of the Crossfires ! I am looking for a good used 250cc on craiglist and online to throw into the other one.

Im wondering how you modified the stock exhaust pipe.
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Old 12-25-2012, 10:21 PM
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I addressed these Q's in the other thread
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Old 12-26-2012, 07:25 AM
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Thanks x. I will try to refrain from duplicating questions in multiple threads. Believe it or not at the ripe old age of 41 this is the first forum ive ever participated in. I usually do LOTS of research before doing whatever it is Im planning but never go further than looking. So you should all consider yourselves very fortunate because now that I have become a joiner......i will annoy you ALL till the end of time. MMMMWWWWAAAAHAHAHAHAHAHAAAAAA!!!!
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Old 12-26-2012, 08:27 PM
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Old 12-27-2012, 10:44 AM
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Just remember, as u gain knowledge, others shall persue you!!!mmmmmwwwwaaaahhhahahah
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Old 12-28-2012, 07:00 PM
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My buggy has a 32t sprocket. I was thinking of buying a new countershaft sprocket as mine is a 16t and if I could get a 13t to replace it then it would be easy to change up between power and speed. Only problem is all the places Ive found to get them are "bike" specific. Year,make model of motorcycle is needed to get the sprocket. That helps me not one bit. If I properly uploaded my image it will show what my sprocket looks like. So wondering if anyone has an idea of how to get one besides going to the local motorcycle shop and paying twice as much as internet.
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Old 12-28-2012, 07:15 PM
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How about making one fit your application?

https://www.*************.com/sort.a...EN=20&PageNo=6

http://tsc.tractorsupply.com/search#...&sliredirect=1

http://www.ebay.com/sch/i.html?_trks...at=0&_from=R40
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Old 12-28-2012, 07:52 PM
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The one on ebay was for a 520 chain and mine is 530. Will it make a difference?
If not Ill get that because it's just what I'm looking for. 3 teeth difference on the small sprocket would make a sizable difference in power wouldn't it?
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Old 12-28-2012, 07:56 PM
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Yes, the 520 to 530 size makes a difference.

And yeah, 3 teeth difference on a sprocket makes loads of difference. (especially on the engine side)
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Old 12-28-2012, 08:06 PM
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You've given me some direction. Thanks x. It's such an easy sprocket to change and I've got alot of chain adjustment. loosen chain, remove 2 screws, switch sprocket, replace screws, adjust chain, and switch from speed to power. Might try to find a 17t also for maybe another 5mph on top. One of these days I'll have some results to post.
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Old 12-28-2012, 08:12 PM
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So 520 sprocket and 530 chain don't mix?
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Old 12-29-2012, 09:18 AM
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520 chain/sprockets have closer spaced links 530 stuff won't seat properly in a 520 or vise versa. The 17 tooth will give more top speed, probably not 5 mph, more likely 3 but it does speed it up.
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Old 12-29-2012, 09:36 AM
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EDIT: I trust Ckau opinion over something I googled on the internet, but, It appears it's just a width difference between the chains. http://answers.yahoo.com/question/in...4074926AAiXoxX

So I guess you could run a 530 cahin and a 520 sprocket?

If you change your rear tire size, you have also changed your gearing. Not alot, but a little bit.

Also keep in mind as you alter gearing engine RPM will change too. If you gear the kart for more TQ, you have raised the engine RPM at WOT. And if you installed a perfromance CDI that eliminated the rev limiter, you can actually over rev the engine and lead to engine failure.

And if you gear it for top speed, you ultimately lower the engine RPM at top speed because you have placed a higher load on the engine amking it work harder. So it increases heat, and may require a carb rejet to help prevent engine failure.

So it's not just a simple sprocket swap per say.....

Hope i didn't confuse you too much.

Last edited by xlint89; 12-30-2012 at 12:00 AM.
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Old 12-29-2012, 02:38 PM
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After doing a bit of sprocket and chain research it seems to me that the 520 sprocket would be thinner than the 530 chain and the chain would have side to side play. I thought of it like 10 speed too. I figured having a 13t to switch out with my 16t would be for areas where hill climbing and short bursts of speed were required and then use the 16t in areas where speed and WOT was in order. My buggy had a 530 chain on it (took it to local cycle shop and asked) but Im thinking the sprockets are not 530 because the chain has lots of side to side play. I think ill wait till I can get all sprockets and chain new so I know what I have will match. Its not like a cheap Chinese buggy would ever have mismatched parts.....Right??
Thanks for the replies.

Last edited by SLESTAK75; 12-29-2012 at 02:40 PM.
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Old 12-29-2012, 06:48 PM
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EDIT:


If you put it on the largest sprocket on the crank, and the smallest on the wheel, you peddle your butt off and go 1/2 MPH. BUT, you have the ability to climb a mountain in that gear.

Now go the opposite. Smallest gear on the crank, and the largest on the wheel, you have the ability to go 30 MPH. However, you have to stand on the preddles at take off, and it takes you a LONG time to get there.

These are the same way. Only instead of the "crank" sprocket, I say "engine" sprocket. And instead of the "wheel" sprocket, it's the "axle" sprocket.

To make things more complicated, if you change your rear tire size, you have also changed your gearing. Not alot, but a little bit.



Hope i didn't confuse you too much.

Hate to pop your bubble, but you've got that bass ackwards my friend

Big ring at the crank/little at the wheel = top speed and a ton of effort to turn. Little ring up front (crank), big at the wheel = wheelies, rock/vertical climbing etc. Take it from a bmx/mtn bike racer with 25+ years of competition/bike building.

For the buggies the engine output shaft and axle sprocket operate on the reverse principal of a bike because the engine has already gone from the variator pulley to the clutch pulley/output shaft sprocket.
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Old 12-29-2012, 08:15 PM
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I think I'm going to weld my axle straight to the crankshaft and not worry about chains and sprockets any more.
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Old 12-30-2012, 12:03 AM
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OOPSY!!!! Thanks X.
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Old 12-30-2012, 12:04 AM
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Let me first ask you what buggy you have. Sprocket changes do not create more power. All you do with sprocket changes is move your power curve. The buggies come set up from factory for all around performance. Larger axle sprocket or smaller output sprocket will increase low end torque. Going the opposite way will give more top end torque. So no matter which you go you will improve on one end but suffer on the other.These motors were designed for scooters of less then half the weight pushing one wheel and driving one wheel. The only way to make more power is to build the engine to take in more fuel and air and efficiently burn it. The average naturally asperated engine only fills 65% of the cylinder with A/F mixture weather it be a car or ATV or Cycle. To make more power you need to mod the engine to efficiently bring in more A/F above the 65% volume. Now as for the sprocket , a 520 and 530 sprocket or chain has both different width and pitch. Yes you can mix the 2 but you will be constantly changing sprockets and chain on a frequent basis.
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Old 12-30-2012, 06:54 AM
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Quote:
Originally Posted by xlint89 View Post
EDIT: I trust Ckau opinion over something I googled on the internet, but, It appears it's just a width difference between the chains. http://answers.yahoo.com/question/in...4074926AAiXoxX.
xlint89 is so correct I gave the wrong info. Please ignore my brain phart
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Old 12-30-2012, 11:41 AM
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Let me first ask you what buggy you have. Sprocket changes do not create more power. All you do with sprocket changes is move your power curve. The buggies come set up from factory for all around performance. Larger axle sprocket or smaller output sprocket will increase low end torque. Going the opposite way will give more top end torque. So no matter which you go you will improve on one end but suffer on the other.These motors were designed for scooters of less then half the weight pushing one wheel and driving one wheel. The only way to make more power is to build the engine to take in more fuel and air and efficiently burn it. The average naturally asperated engine only fills 65% of the cylinder with A/F mixture weather it be a car or ATV or Cycle. To make more power you need to mod the engine to efficiently bring in more A/F above the 65% volume. Now as for the sprocket , a 520 and 530 sprocket or chain has both different width and pitch. Yes you can mix the 2 but you will be constantly changing sprockets and chain on a frequent basis.
Enter the Grammar Police. I must start by explaining that I lack the ability to type with speed and accuracy and therefore often prefer to explain the thoughts of my head in short terms that the majority would have the ability to understand by applying common wisdom. I must apologize for this shortcoming and endeavor to explain my thoughts with greater clarity. I certainly never meant to imply that by changing a sprocket one would miraculously create more power in an engine that was untouched and unchanged by the alteration of said sprocket. I merely wished to express my desire to have a variety of sprockets to choose from in differing situations. A 13t that would benefit me in a situation where I may be climbing hills and would not be adversely affected by the lose of top end speed and a 16t which would be desirable in situations where greater top end speed was a possibility. For those who didn't understand my post I will attempt to help you understand. By changing the drive sprocket this would lower the top end speed at Wide Open Throttle. This results in less strain on the engine when delivering its power to the wheels. To illustrate: If you have ever tried to accelerate from a stop on a 10-speed bicycle while in the highest gear, you have experienced the great strain that this puts on your muscles; however, if you change to the lowest gear the strain is gone but you don't go as fast. This is in no way is meant to imply that by changing the gear you instantly have more muscle mass. In this way there is a big difference in creating power by building the engine and reducing the strain on the engine by lowering the gear ratio. I could imagine that this could be perceived by some as an increase in power due to the greater and more instant throttle response. For those of you who were offended by my gross misuse of the word "power" I offer my most sincere apologies. Please know that in the future I will apply myself to better explaining the thoughts in my head. If; however, I chose at some future point "not" to spend 30 minutes typing out a thought that i could explain in a few short sentences that the majority would understand, then please feel free to correct me again. Or if you so chose please ask my to clarify my thoughts and I would be glad to do so. I am only human after all and I am bound to err again. As to the thoughts on the 520 530 chain sprocket issue, the sighted article explains that the "pitch" of 520, 525, and 530 chains is 5/8". As to the validity of this article I can not comment. But other information that I gleaned from made to order sprocket manufacturers seemed to support this line of thinking. If I am incorrect then I blame it on the blatant falsehood of information on the internet, or my inability to understand that 5/8" is different on different chains and sprockets. In either case I must again extend my most sincere apologies and hope you will accept that I will do my best to refrain from future infractions such as these. I am grateful to have found this forum and truly appreciate the efforts of those who endeavor to expand the understanding of those of us with less experience. Keep up the good work .

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Last edited by SLESTAK75; 12-30-2012 at 11:53 AM. Reason: left one thought out
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Old 12-31-2012, 02:32 PM
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After taking a caliper to chain and sprocket they are definitely 530. Chain stretch is why I had play. So if I put the 520 sprocket on I would end up with quicker wear due to the thinner sprocket SOOOOOOOOOO. I guess I will see about having one special made. Thanks for the advise.
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Old 01-05-2013, 07:59 AM
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I do believe I know why I have had such a problem finding this sprocket. It is a 16t "reverse" sprocket. It has a 25mm shaft and all the "drive" sprockets I've seen have 20mm shaft. Might try going to the machine shop at the local vocational school and see what they can come up with. If it doesn't work I wont be out anything.
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Old 01-05-2013, 08:41 AM
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Check with Tom @ syc, I think he can get u the reverse sprocket if thats what u want to go with.
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Old 01-05-2013, 02:10 PM
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I might give that a try. I want a 13t and a 19t that will fit so I can change out for different situations. I will see if Tom can help.
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Old 11-09-2014, 10:16 PM
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I'm getting to the 300' mark going 43mph at 8400 rpm, but my engine is still pulling @ 9200 rpm so I figure the 3:90 ratio will get my rpm's up faster thus getting me there faster and in less time. But I'm sure I will also have to add weight to the cvt as well. My buggy will top out about 52 mph. I'm working in the 300' range since what I want is the quickest burst I gan get. Most trails have bumps and curves and on average speed ranges around 25 to 30mph and that is pushing it. But when you get to a strait the atv's will pull away from the buggy. This will give me more power to keep up with the atv's, plus I like to drag race and every bit helps.
Dam... That's cooking!!!!!

Finally got around to getting a WOT run with the new mods installed.

My mods are all posted in my sig. All stock CVT

Pulled a 32.7 MPH 300' run backed up with a 32 MPH 300' run.

Top speed measured 40.2 MPH

I finally made it to 40!!!!
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Old 11-09-2014, 10:19 PM
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I know you asked T3, but I've kept pretty good records of my performance gains after each modification to my Yerfdog 3206.

Stock Spiderbox configuration: 13/40 internal gears, 13T engine sprocket, 31T axle sprocket, and 743 20 30 Gates belt.

All measurements were taken with a Garmin Etrex handheld GPS, on concrete, with a set distance (approx 300'), on the same "track".

22.3 MPH as is from previous owner (stock tires, slightly deflated, stiff front suspension)

23.1 MPH performance coil, performance CDI (both orange from Ebay), no air filter and 125 main jet

23.7 MPH opened muffler opening (1/2" stock VS. 3/4")

24.9 MPH home ported head and port match intake manifold

26.3 MPH MAX SPEED (first run on street)

25.2 MPH 10g Dr. Pulley sliders with cleaned/lubed CVT, and deglaze clutch and bell

29.8 MPH MAX SPEED

26.8 MPH New tires and bearings (22" rear), FMF slip on exhaust, UNI air filter with 6" extension

33.2 MPH MAX SPEED

27.2 MPH 8" extension for air filter

33.0 MPH MAX SPEED

28.0 MPH NCY CDI (orange with aluminum housing)

33.0 MPH MAX SPEED

All readings were taken with all upgrades added to one another. Only the air filter extension was substituted.

Round 2 Test and tune


28.6 MPH 12 gram Dr. Pulley sliders and header wrap for 7"

35.3 MPH MAX

30.1 MPH A11 cam installed (needs larger pilot jet)

38.9 MPX MAX


Last test and tune session with basic "stock" engine:

29.6 MPH with stock rollers
37 MPH MAX

30.2 MPH with Dr. Pulley variator and 12g sliders
38.3 MPH MAX

I tried getting readings with a 6", 7", and 8" red neck tube extension, but they were all around the same speeds in accel. I didn't have the jetting nailed down yet with the A11 cam until after I made the passes. The kart was blubbering off the line.

Ended up using 35 pilot, 2 1/2 turns on the mixture screw, and a 122.5 main jet for good reults.

So no improvement from the last test session. 12g sliders in the stock variator seemed to work best for me.

OK, so now I have the 62mm BBK kit installed

32.7 MPH in 300'

Max speed 40.2 MPH


Time to install the good stuff......
Bump to the top to reflect on the mods that got me where I'm at thus far
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Old 11-10-2014, 07:28 AM
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My biggest gain was the custom cam I had ground. The grind has a 34 deg. overlap so lots of duration. The available performance cams don't come close. I also had to up the carb to a 32mm mikuni slide carb. The down side is I will use a tank of 103 octane fuel in about 2 hours of trail ridding, also when cruising my RPM's are quite high. I need to regear the final drive to bring the rpm's down and give me more top end on the long runs but I have to be careful not to sacrifice too much bottom end.
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Old 11-10-2014, 06:33 PM
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How much was the custom cam?
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Old 11-11-2014, 09:07 AM
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Some where in the 200.00 -225.00 range. The hard part is getting the sprocket in line with the cam using a degree wheel and dial indicator since the sprocket on these cams are pressed on.
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  #97  
Old 11-11-2014, 05:51 PM
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xlint89 xlint89 is offline
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Too much $$ and too much work for me then. Thanks Tom
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My Yerban assault vehicle: 2.2mm stroker crank, 62mm Nikasil cyl, Taida large vavle head, American made valve springs, ported intake manifold, TM 28mm carb, stock CDI, Bando coil, TK exhaust, stock CVT except for the 14g sliders, 13/40 internal gears, 16T drive, 31T axle sprocket, 22" rear tires, and ONE BIG POTATO CANNON mounted on top..........
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  #98  
Old 11-11-2014, 09:19 PM
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SYCARMS SYCARMS is offline
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Well all the work you will have is installing, I would degree it before selling. The available performance cams will work fine being out as much as 10 degrees. With the amount of overlap this cam has it is much more critical for if out 3 degrees performance will suffer. Before this cam I had a killer engine. After installing the cam which I expected more power but was totally surprised at the added power. I had to get away from the 32mm CV carb and go with the 34mm Mikuni. As I always say the more air and fuel you cram into the cylinder the more power you will get.
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  #99  
Old 11-12-2014, 07:13 PM
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xlint89 xlint89 is offline
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Are you looking to sell your cam? That's what it kinda sounds like.....

I know about the more air, the better. Funny though, I remember you and another guy trying to convince me the stock carb was best until you went way bigger engine. That was a few years ago though.

I too like my Mikuni flat slide. very responsive.
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My Yerban assault vehicle: 2.2mm stroker crank, 62mm Nikasil cyl, Taida large vavle head, American made valve springs, ported intake manifold, TM 28mm carb, stock CDI, Bando coil, TK exhaust, stock CVT except for the 14g sliders, 13/40 internal gears, 16T drive, 31T axle sprocket, 22" rear tires, and ONE BIG POTATO CANNON mounted on top..........
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  #100  
Old 11-13-2014, 06:30 AM
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SYCARMS SYCARMS is offline
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No I'm not selling my personal cam. Back when I was running the 61mm bore with A8 cam I run the stock carb. I still run the stock carb with the 4 valve head. It was only after I installed the 6mm stroked crank with 62mm bore and large 2 valve head that I went with the 30mm carb. I then had my 62mm bore sleeved to a 63mm and ported the large 2 valve head but still used the 30mm carb. My sons buggy in the meantime we built with a 3mm stroked crank my old 4 valve head, running the stock carb. My next step was to have the cam reground and after installing found I needed a larger carb since the 30mm was not getting things done, so I went to the 32mm pump cv carb. I had to run a 46 pilot and 190 main but it lacked in 2 areas. Accelerating from a dead stop I had a dead spot (hesitation) I could not get rid of and after a WOT run my plug was a light tan. I went with a larger main but only saw my mid range power suffer. This is when I realized my carb needed more CFM's and the fact that I had 34 deg. overlap this made the CV carb obsolete since the slide relies on vacuum to operate the slide would no longer efficiently react to a rapid acceleration. This is when I went with the 34mm Mikuni. A carb is not only chosen from amount of CC's. alone since a carb size is chosen for the amount of air the engine pulls through the venturi. When a carb is too large the negative pressure needed to pull the fuel up through the main jet is not sufficient which is one reason some people run larger mains then others to compensate but efficiency is lost.
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