Keihin cvk 30mm pumper carburator

[ckau]

We finally got the chance to play with a keihin cvk 30 mm pumper carb. A Dazon single seat 150 ,stock motor except for a bugle style header, straight through muffler and a uni with velocity tube was used for this trial.
First challenge was to get this carb mounted properly. There are spacers and intake extensions available but we didn’t like the idea of having the carb up above the motor mount bracket plus extending the intake runner length by using these extensions was not the best way to gain advantage out of this carb. We felt this setup would create tuning nightmares base on the complaints we have heard from other who have tried using the extensions Erratic idle, bogging and inability to get jetting correct. The optimum intake tract length for the gy6 is approximately 14.3 inches measured from the end of the velocity tube, through the carb, down the intake ito the head valve seat. It stands to reason when the tract gets too far out of the optimum range of length there’s going to be some issues.
Rich1, [buggy owner]\ came up with the brilliant idea of torching the plastic covering off a stock 24mm gy6 intake then fabricating an adapter conversion tube to mate 30mm carb to the stock intake. This “ conversion tube” gave the ability to fit the carb in the original location plus the ability to adjust the intake length if needed. The throttle cable had to rerouted and the starter housing was rotated to move the electric connection away from under the carb. It’s tight but fits!
I had suspected for quite some time these 150’s were under powered with a 24 mm carb . I felt the 24 was used as a matter of convenience and economy rather than from a performance stand point. The 30 proved this opinion to be correct!
We were astounded by the performance gains! Throttle response is crisp and instantaneous. Zero throttle lag at any speed! Motor turned almost a even 1,000 rpm more than ever before. Top speed increase by approximately 7 mph. Acceleration is smooth and strong. Top end speed is now only limited by the gearing. This buggy is now a real handfull to drive. We had to learn the characteristic of this buggy all over again. Whereas we used to anticipate throttle lag in turns , response is now instant . It’s too easy to overpower when accelerating out of turns.. It proved difficult to prevent wheelspin at times. Good brakes and proper braking techniques now comes into play. Rich1 commented “Oh great! Now we got to figure a shock setup that’s gonna keep the rear end on the ground!”
Jetting the 30mm really fooled us. Figured on something like a 135 or 40 would be sufficient but we ran out of jet sizes at 150 and it is still a touch lean. Didn’t worry too much about the pilot/slow jet at this time cause the pumper circuit would compensate for any critical adjustment temporarily. A set of main and pilots in the larger jet ranges are ordered so the fine tuning can be completed. It will be exciting to see exactly what can be had from this carb. I’ll give an update after the jets arrive.

[GX150]

I am assuming your petcock and fuel lines are already upgraded? I was running a 150 main until I was able to get fuel faster out of the tank. When I had better delivery, a 140 main was sufficient.

[rich1]

Good point...I was ready to increase the fuel line before the basic testing started.But the stock gas line is some where between 5/16 and 1/4 " on a Dazon.The new Tygon gas line seems to be slightly larger still and will be used on the next test trials.Since the pumper is spraying gas into the carb before the slide even moves the lean stumble down low has vanished. The motor is not starving for fuel but instead its simply burning all of it threw better metering.

[GX150]

I reamed out the fuel barbs on the carburetor and petcock to maximize I.D. then ran 3/8" fuel line and filter.

[rich1]

Correction on OPs post .The current jetting is 145 main and 40 pilot . The exhaust being used on this project is the bugle or paper clip pipe. This pipe that was used in 4 cycle Briggs kart racing is known for its superb exhaust scavaging but it very sensitive to jetting changes by 5 points and works better on the 3 point scale.

[rich1]

Update for tuning...I tried to see if the set -up would now run a 148 main which is just 3 points richer, no go. The motor started emitting black smoke at full throttle so back to the 145 . However the pilot jet still seemed a little rich at 40 ,this stands to reason since thats what the 250 motors use.The air screw on the carb was not providing very much mixture adjustment, which usually means the wrong size pilot. So back to the jet box to get a 38 . Now this is better , at 1-2 turns on the air screw the motor is crisp and has a steady ilde.The plug color is now looking like a med gray color on the white insulator 1/4 the way down now.I never tune an engine with the Uni outer filter on either ,its better to get the jetting a tad lean so when the outer filter is used it will be a little richer anyway. BTW I have always found that the regular copper NGK plug is best to do jetting changes with. The fine wire plugs are hard to see color and burn hotter than normal too.Those plugs are ment to last a long time but do not conduct voltage as well as copper.If you can jet the carb properly then you dont need an 8 dollar plug.When you need to clean a plug just use a spray cleaner and a Brass brush , never use a steel brush or sand blast a plug. The reason is once the insulator is scratched or pitted it will hold carbon particles and foul easier.
Next step is to measure the spark output/ volts to see if any hotter spark is really needed. Stay tuned.

[GX150]

Since you dropped down on the pilot size, you may be able to run that 148 main now. Remember that the pilot is always providing fuel and the main adds to it over half throttle...

[rich1]

Originally Posted by GX150

Since you dropped down on the pilot size, you may be able to run that 148 main now. Remember that the pilot is always providing fuel and the main adds to it over half throttle...

Exactly...thats the goal to run as much gas as the motor will stand to keep it cool.However according to the Mikuni Tuning Handbook, pilot jet only effects 0 to 1/4 throttle. (I was reading an OEM source the other day that talked about the overall fan cooling system.It said that not enough cooling was being provided and that 1/4 of the cylinder/ head was not cooled at all.) Furthermore if the displacement is increased that the motor was subject to being overheated to the point of failure ,if not closely monitored.
Anyway, if not enough spark voltage is avaliable to burn a richer mixture overheating results anyway. So now its time to measure the spark voltage and see.

[SYCARMS]

Don't understand why 1/4 of the head is not cooled when the jackets run throughout the whole head. When I check mine using an infared thermometer the temps are consistent throughout the entire head.Also I have not had any problems with my big bore kit making it run hot. If pushed hard for a long time it will get warm arounfd 200deg. but this I believe to be due to the inadiquate radiator capasity.

TOM

[rich1]

Coil testing...I decided to see if a performance coil did any good at all.

.Here are the results.

Stock coil and CDI... 20,000 volts
Orange Aftermarket coil and stock CDI ...25,000 volts
Yellow Aftermarket adj.CDI and Orange Aftermarket coil...27,000 volts

Ok as you can see the stock coil is weak.The reason this is bad is because the NGK fine wire plugs take MORE voltage to fire than the NGK copper plugs do . The GY6 ignition uses a system that fires the plug for every complete turn of the crank which is 2 times for a 4 cycle . This type of system is called a wasted spark ignition and does not give a long dwell time in order to fully charge the coil windings.So I decided to use the Orange coil and the NGK Copper plugs to help avoid mis-fire while doing the next step ..which is testing for the best gas octane to use.

[rich1]

Originally Posted by SYCARMS

Don't understand why 1/4 of the head is not cooled when the jackets run throughout the whole head. When I check mine using an infared thermometer the temps are consistent throughout the entire head.Also I have not had any problems with my big bore kit making it run hot. If pushed hard for a long time it will get warm arounfd 200deg. but this I believe to be due to the inadiquate radiator capasity.

TOM

Sorry Tom...The fan cooling system that the source refered to was the stock GY6 forced air system, NOT the water cooled motors.

[SYCARMS]

My brain farted, if I had read the post more carefully I would have seen the topic was a 150. At least my head feels better now.

TOM

[ckau]

Originally Posted by SYCARMS

My brain farted,TOM

It good to know someone else besides me suffers from this afliction

[SYCARMS]

OH! but it comes with age........

TOM

[rich1]

So according to the Turner,s" Handbook Tuning Manual" the general guidelines for octane usage for Compression Ratios are..

8.0-8.5 ..87-89 octane

9.0-9.5...90-91 octane

10.0-10.5...91-93 octane

Dazon lists the GY6 compression ratio for their motors at 9.5:1. So it is at the 90-91 octane rating scale for this stock motor. However some GY6s have more and some have less . If the motor is modified or has a little carbon on the piston that can change it too. I have been using 87 for a while because the motor was stock and it is cheap. Now modified... i am going from the bottom to the top levels to find the best one to use. Sometimes you need something in the middle so you blend it by mixing 1/2 gal to 1/2 gal. Lets say you want a 92 octane gas just mix 91 and 93 together. With grades from 87 to 114 this may take a while.

[rich1]

More info on gas and tunning...
Most people correctly use plug readings when tuning a motor. But what are they looking for and what is best? The plug color that has been used was a light tan on the insulator tip ,right? Not exactly..that was the old method before Unleaded gas . The Lead in the gas would burn and produce the tan coloring on the plug.So No lead, no tan,the new color to look for on the insulator is Eggshell to an Orangish White color. That means if you find tan or brown on the plug tip then you are running a little rich to a very rich condition. Now that takes care of normal gas ,but what about the 10- 15 % Ethanol mixed "Winter" gas. Those plug readings will show a slight graying of the insulator to a cigar ash like coloring when viewed. Like i said before, yes you can read the fine wire plugs while tuning but its alot easier to view the thicker Copper style ones.Furthermore..
The copper NGK plug has a wider flame path than the fine wire NGK plugs do, about 0.80 wide vs 0.32. electrode thickness.

[rich1]

Buggy is running very well but it spins the rear tires too much with this Bugle exhaust. So now what? Well i could re-gear it but the gearing is right for the trails and the track. Ok lets just move the powerband a little from low to mid -range with a different exhaust. I going to built an exhaust from an old Hammerhead Twister stock header.But.. This is a Dazon so a little modding needed on the header flange . Just cut the pipe near the flange a install a split sleeve . Put a small crimp on each end and re- connect the header to the head. Now line everything up and tack weld, remove and finish the welding. After calling and talking to White Brothers they said that they used a FMF Turbo core muffler on the exhaust they built for Dazons hop -up kit. So i called Big-E and ordered one with an 1 1/4 inlet . I cut the end off the header pipe to fit the muffler inlet and secured it with 2 hose clamps. I then made a bracket to attach it to the case bracket nut. Nice i can remove the VT cover by just removing only the muffler now. Next ...tuning for more mid /top end power.

[rich1]

Ok its been a while but good progress was made. The new pipe is working very good, but the cv was not keeping up. The stock rollers are 14 gm, so i tried some 15 gm ones but the motor was not reving up quick enough . Since i was having trouble with the stock rollers flat spotting, I got some new aftermarket 13gm made out of a synthetic rubber. I installed those along with a new belt . The power band is now stronger in the mid range where most of the driving is done . This seems to match the pipes range better too. The gearing is still stock Dazon... 16 /31 and tops out at about 35mph. Since the tires are still the ones that came on it its time to get a new set . I have an extra set of wheels that I can use and test with too. So now im looking around to see whats out there in the sizes ...
Front 21x7x10 and Rear 20x11x10
So.. any brand better than others ? I was thinking about Kenda Klaws since the dirt here is hard packed dirt and gravel.

[SYCARMS]

Those would be a good choice. I also like the mud lights which work all around especially if you were to drive the mud or sand.
TOM

[metalstudman1]

I run the standard ITP holeshots on beadlocks front &rear 4-ply(the cheapest ones!)Can't hardly do a donut now.They're awsome in all terrain-especially our NC red clay.I had Kenda's on the front before and the ITP's are just as strong getting a good bite.

[rich1]

Its been hot in the 90 -100 degrees here ...but i finally got the Kendas installed F and R, these tires work very well. The old tires where Chin Shin ..Kenda copys they did not hold air well . I used a can of fix a flat in each just to keep them from going flat. The Kendas are not leaking at all. However,the old tires were 4 ply in the front and 6 ply in the rear, the new ones are 6 ply all around. Thats not really a problem but this single seater is very sensitive to weight changes on the front. I reset the front wheel toe in to zero.Steering is good but the extra ply on the front tires is throwing the old tire psi out of range . The pre load on the springs is a little off too .Now its back to adjusting both of those up and down to get it dialed in. Its always something!

[ckau]

rich1 ain't joking , the heat has been murder with extreme humidity too! these small air cooled motors don't like this heat at all! You can run for 15 to 20 minutes then the excessive heat starts robbing horsepower. plus the track is so dry the dust clogs the air filter in a matter of minutes. These motors are so sensitve to air/fuel ratio changes a clogged filter will throw settings off fast. It's difficult enough to endure the heat let alone get something dialed in.
we gotta get a water truck!!!

[SYCARMS]

You guys are absolutely correct this heat is not friends with air cooled engines. These engines will run @ 340deg on a good cool day. Oil collers will help if installed, and oil is very important. Most think that Mobile 1 or Royal Purple is the best for their engines. This is true if the type of oil used is for air cooled engines. The automotive oils are designed for engines that run around or slightly above 200 deg. F. Once that temp is reached the oil reached its thermal breakdown. This is why we all should be using the V-Twin or ATV, Motorcycle oils designed for air cooled engines for they are designed to run @ higher temps then the automotive oils. I have now in my shop an engine which I built 2 years ago where the piston has started to melt down due to excessive heat after being driven long and hard in 100 + temps. This has been an unusually hot year around parts of the country so these engines need to cool down from time to time. The plastic shrouds on these engines have to be on and in good shape to allow air to flow through the fins of the head and cylinder. When you wash your buggy, especially after riding in mud or high dust conditions, make sure to run the water up under the shroud to get any excessive dirt or dist out of the fins. This helps to keep the engine running better. And as stated earlier make sure you use the correct oil for air cooled engines. Oil coolers also help big time with cooling the oil. And never run cold water on a hot engine.

TOM

[rich1]

Got to agree with Tom on this one...I run Pro Honda Motorcyle oil (10W40) in my buggy for that very reason. I also run it in my motorcycle , golf cart, generators, lawnmowers,and tiller ...anything that is not water cooled. I have been doing this for years without any major engine failures.The other advantage using motorcycle oil its designed to be used in a gearbox and has a better sheer strength than regular oils do.

[rich1]

Someone PMed me and asked how align the front end...Cliff notes version.
First see if there is any play in the steering ,if so stop and fix it .Since the toe in/out adjustment is only about an 1/8 " total,so this a quick set /check for the field only !First set the tire pressure the same for all 4 wheels. Now turn the steering wheel till centered and lock in place if you can.Then look on the front tires for the mold casting line down the center.Using a tape measure,at 3 oclock back of the wheel, measure the distance from the Left wheel to the Right wheel mold lines. Write it down , then do the same at the 9 oclock on the front of the wheel . The difference between those 2 measurements will show the toe in reading .Loosen both L&R tie rod sleeves and try to adjust both at the same time to keep the wheel centered.When the front of the wheels are further apart than the rear of the wheels that is toe-out.Set to desired toe and tighten sleeve nuts back up. Check again to be sure !Thats it .
( Confused? Stand up and point youre feet straight ahead ... Zero toe.Move youre feet in ...Toe in. Move feet out Toe out !)
So.. If the measurement is the same for both then the toe is Zero. I like Zero toe settings since i used to Roadrace Enduro Karts up to 135 mph.Besides,most of time if you have to use toe settings to correct bad handling then the chassis is not set up right. !
Note... Toe out 1/16 ...will make the steering tracking wander at speed. Toe in1/16.... will make the steering tracking quicker. Zero toe will give netural steering .
Thats it for toe settings only ! Since it is the last measurement done on a front end alignment it is asumed that all other measurements were correct !

[rich1]

So the Kendas front and rear are fine . These are 6 ply tires so i had to lower the air pressures from 15 to 10 lbs. Steering is still crisp and does not bounce as much with the lower pressures . I may go down to 8 lbs next but the track is still dusty since rain has been hit and miss. I still wish i could regear within 2 teeth on the rear or 1 on the front larger . The FMF pipe pulls better on top end than the Bugle pipe but im only turning 7,500 rpm . Just 500 rpm more would be perfect. Dazon uses double row sprockets but i cant find any but the stock ones, 16/31. I do have the parts to go to a single row sprocket setup if I can find any sprockets. Loooking for 17 front or 32-34 rear any ideas whre to find them ? BTW... Has Hammerhead style rear axle and reverse.

[SYCARMS]

I have the 34 & 37 tooth double row sprockets in stock. Give me a call,662-301-1563 or e-mail me.

TOM

[rich1]

The upgrading continues.. This mod was long overdue i have Works shocks on the front of the buggy but not the rear. I have been trying to use various sets without any real sucess. So i finally broke down and got a set of Works for the rear. I made some brackets to mount the shocks since they are 14.5 in. long . That worked fine since i gained a full inch of travel too.They are 2 stage spring sets using the short Black ones on the bottom. The problem was they came with straight wound main springs that were way too stiff Blue 90 lbs . I was losing half the travel i was supposed to have, so I changed the springs to a Yellow progressive set . Next i set the pre-load to the standard 10mm the result was 5 in of controlled travel and no sag. Since this buggy uses a rising rate suspension with the rear higher the steering ackerman has been greatly improved too.. So Sun. was the big shake down test day ! The track thru the woods has a 2 foot high down hill jump that I always let off for in the past, not today. It was like it was not even there plus take off traction improved since the rear now squatted and got traction. However just when all was great the rear axle shifted and ground to a halt. One rear axle bearing failed and gauled the axle beyond repair. The axle was not exactly cheep either, the best price i could get was $160.00. Dam I was going to put new bearings all around over the Winter I guess the plan was moved to the Fall instead. Thats Racing !

[rich1]

Well ......I got the rear axle changed. The original bearings were sealed just on one side , the new ones have seals on both sides,nice. I was going to change the rear gearing but does not need it now,the old bearings must have had alot of drag. Buggy is fast on the track and in the woods .Longer rear suspension travel is great with about 5" of dampened travel.I say get the longer shocks like i did and make a set of brackets.The longer 14.5 "shocks have alot better selection of springs too. However i just used a set of HH springs and still have another pair to try if needed. Since the Works shocks control piston travel both ways , I am using a set of progressive wound springs instead of the straight ones. If you use these springs the rate of travel will be alot more controlled all the way around.BTW.. If you have not tried a better set of shocks you are beating your buggy to death.

[metalstudman1]

So did you by-pass the 2' jump this weekend? Was your axle bent along with the field welded bearing? I wish I could afford some Works or Fox shocks!!! even used ones are very expensive- it's hard to justify. But I absolutely agree that we're beating up our karts without them. What's the seat diameter on the progressive springs? I've been hunting for a set of 1-5/8" that would fit my Carrera hyper shocks, they have 7" of travel but I don't weigh enough even when jumping to use all of it, My lightest yellow springs (80 lbs.)are too soft (too much body roll)and my gray (95 lbs.) are almost too stiff but handles well in the trails.

[rich1]

No way,and the jump was just fine again. The bearing surface was damaged and the axle was not bent. However I had another rear axle from a HH that i was going to use but it was bent ! So new axle time. The springs came off a set of shocks from a complete HH Buggy I bought for parts. Ill have to check the size of them and let you know since they are at the shop. If you break enough parts from bad shocks you will have the Works or Fox shocks paid for !
We are starting to do a complete overhaul of the Track and the Trails.
We just re-graded the Track base surface and set it at a 15 degree angle all around. The turns are going to be banked and wider. The straights are going to be wider and shorter .The middle surface will be packed and the top surface will be very smooth. The changes to the track will make it a very quick track and give lots of room to pass. The Overall shape will be more of an O than an Oval . It will be more of a Drivers track than a Drag strip !

[SYCARMS]

A set of custom shocks such as the Works are extremely expensive compared to a stock shock, but they will give the buggy such a better ride and handling you will literally have a new buggy. I sold a set to a customer earlier this year and due to his experiance and word of mouth I have sold 2 more sets. Words alone cannot describe the difference the shocks make, and even after investing the money on these shocks the total cost is still less then a named ATV.

TOM

[metalstudman1]

Ya'lls track is awesome.I wish I owned the machinery to improve on my track as it's getting rough!!! I'm hoping one of my nice neighbors will come box mine smooth again!!!

[rich1]

Finally ..The new track is finished!Sorry no pics yet (Ckau`s job)

The track is banked about 15 degrees in the turns and about 16 feet wide. Straights are a little shorter but you can go faster, longer since the turns are now banked.The surface is made up most of a granite yellow gravel that packs tight and drains well. We made a drag screen that is 8 ft wide and 10 ft long to drag on the track like a baseball infield being preped. We found out by doing this the grit in the track comes up to the surface and gives alot better traction with less dust. Its FAST too you dont have to back off till the middle of the turns now if any. The axcess road to the track was also improved so that it does not wash as bad after a rainstorm.
The next project will be to improve the trails in the woods and make them longer for even more fun !

[rich1]

Just announced... Project Sledge - Hammer ! This will be a built 2005 150 Twister motor with the following mods....