Regaining lost torque
 

Hey guys. I recently installed a uni filter and jetted to a 130 on my ASW Quantum. It seems like I have gained some top end but lost on the bottom end. It's pretty noticeable with two people riding.

I will be picking up some 12g sliders in the near future but was curious if you guys thought I may notice a difference with a new cdi? I've read a lot and it seems some people love them while others are not such big fans.

I hate to ask the same questions that have already been asked but I'm looking to establish myself in your community and hope to enjoy some dialogue with you all.

Thanks

Might suggest go back to your other jet. Most times just changing air intake, won't require new jetting. Was your jetting off, to start out with? And was that jetting it up or down? Guessing up. But never know.
If your looking for lower end. I'd suggest 11g sliders. You will still hit your top speed. Just take longer.
If you did happen to jet down. Then guessing it's starving at higher rpm.
If you jetted up. Could be flooding slightly.
Don't know if new cdi will help.
Make sure you got good connections on your coil. They might be attached. Make sure they snug.

I think my jetting is okay. The bike runs well and the plug looks good. I've just lost a bit of bottom end on take off. Seems to pick up in the higher revs.

From what I've read the 12g sliders seem to offer the best balance for me. I should gain the bottom end of a 10g roller without losing on the top end very much, to my understanding.

Welcome to the site.

I'm guessing you removed your old OEM air box to install the UNI filter?

If so, did you install the UNI directly to the carb?

You may need to install a length of pipe between the carb and filter.

About 6 inches is what most people use.

I added roughly 6 inches of pvc between the new uni and the carb. Thanks for the reply.

Xlint89, in your experience do most people notice a gain in bottom end when simply installing a new filter and re-jetting? I did feel like I gained some in the top end.

99% of my experience is with bigger car engines (been around drag racing since I was a kid and building v8 chevys since I was 12) and I'm not Xlint89 but most engines you will only notice any benefit from opening up the air flow in and out in the upper RPMs. That said yes if the intake or exhaust is grossly undersized then yeah you will notice it in all RPM ranges but on most gy6s its not the case.

The reasoning behind this is if you think of the engine as an air pump at idle it doesn't require near as much air as it does at say 8k. I can get into the black magic of restricting the air in the exhaust more commonly called back pressure and yes that does move the power band down lower but we were talking about opening things up.

Again from experience you don't notice any real gains with bottom end unless you do something mechanical. Could be cam, slidlers/rollers, gearing, or so on.

HP and torque is a balance scale. Its easy to add to one side yet it almost always removes from the other. It's much harder to add to both and get an even result. That doesn't matter if its a 3hp briggs or a 575 chevy.

I plan on installing 12g sliders in the near future. Hopefully I will notice a small improvement in torque. Still wondering if anyone can chime in on the CDI upgrade? Thanks for the input Neo.

best thing I've found for the cdi upgrade is this video.

https://www.youtube.com/watch?v=p63JXW29tVo

He does real tests and not just "seat of the pants" crap

Thanks, I'll have a look right now.

good luck, I'm still tinkering with my 150cc but the 400cc sitting in my shop it looking better every day

I can only imagine. I realize that I will never turn the 150cc into a tire spinning, trail chewing monster but if I could just eek out a bit more power then I would feel a lot more comfortable going out with a passenger for the day. I likely wouldn't mind as much if I weren't planning on riding with my wife, but it's more fun with a passenger anyway.

Oh trust me. I used to jump out of a 8 second 1/4 mile chevy luv when I was 16 into a 4 cyl honda accord to drive back and forth. That was before the whole ricer crap and nobody made go fast parts for them. I drilled out the jets in the 3 barrel carb and welded up my own header for that POS.

I have a 9 y/o that I screwed up teaching how to drive my 5 speed v8 s10. I think that little SOB is worse than his POS daddy at that age. Dad used to complain about my need for speed hands him the keys and laughs at him cutting donuts in the pasture.:banghead: Then again we are talking about the same 3 y/o with add that payed enough attention to us turning down the throttle on his 4 wheeler he went out in the middle of the pasture and cranked the screw all the way up on his own. One of those proud daddy moments you can't be mad about but you just know you better put the ambulance on speed dial.

It may be that you haven't lost any real bottom end but the mods you preformed improved the top end such that the bottom end now seems to be lacking. You have shifted the power band into the upper RPM range. The jet size you chose seems a little excessive for just a air filter change. you may be able to achieve a better balance by lowering the main jet and going up a touch on the pilot jet. There's no set rule on jet size when altering air/fuel. it's all trial and error.

I was wondering about the pilot jet and whether or not I should experiment with it. I will pick up a couple of smaller jets and do a bit of "testing". I guess I figured I wasn't too far off simply because I haven't noticed any issues with how she's been running and my plug colour seemed good. Can't wait to get a set of sliders in there. I need to get ahold of SYCARMS and see if he can help me out with the lower control arm I need and some sliders. I'd like to keep money in the "community".

I hope to keep an open chat with you guys. I found a lot of information here to be very helpful and I hope the next guy in my situation can learn something from what we discuss.

Neo, keep an eye on that one. Make sure he learns how to work on his own junk so he doesn't have to beat dad's good toys all to hell. Sounds like you've got your work cut out for you. :drive:

With the UNI installed now, have you tried adjusting your idle air screw?

Count how many turns (and partial turns) IN until it lightly seats and record that.

Then put it back to where it was set and try adjusting it up and down 1/4 turn until you get your highest RPM at idle (on a warm engine)

See what works best. You may find you might need to rejet the pilot as noted above.

If you feel there is little to no difference, you can set it back to where it originally was at with no harm or $$$ spent.

I run a NCY CDI on mine. It doesn't seem to do much over stock, but it does make it idle slightly smoother.

One of the mods I think did help mine on the bottom end was the performance pulley. It's advertised to gain more top speed (which didn't seem to be the case for me), however, I did notice a better take off with it. I already had the sliders installed too.

OH, and the biggest performance gain I noticed was port matching the carb to intake manifold, intake manifold to head, and head to exhaust pipe. It's amazing how far off those pieces can be due to mass production. Once again, costs NOTHING to do this and made a big difference in stock engine performance.

Adjusting the valves can make a huge difference in low end torque.

I will play with the idle a bit here shortly and see if I can find a sweet spot. I put the 130 jet in after reading a lot on the forum. It seemed to be the most recommended. I did read that most had a 114 main from stock but the one I removed was a 108.

I will have to price the pulley through SYCARMS as well as the sliders and control arm. As far as the port matching, I did a little reading on it last night. That being said, I need to do a lot more reading lol. I'm just in the midst of building a nice new garage so I will have lots of room to tinker now.

Liduno, I've seen lots of talk about adjusting the valves. The Quantum I picked up only has less than 400 miles. Is that still something to check out at this point?

Thanks again fellers.

How about a pic of your set up please?

Many times guys come on with similar issues only to find they didn't plumb the vacuum hoses properly.

I'll get some pictures up soon so you can have a look.

With just a cold air intake, you should be jetted around 122 or 125 for your main. I think 35 was the stock pilot size and you may be able to go to 38 or it was 32 and you can bump up to 35.

Thanks for the info. I need to do a bit of testing. I haven't noticed any bogging or anything else and my plug color seems to be good. I think I will grab a fresh plug today and do a few runs and see how it's looking. Unless I notice the bike struggling and bogging or have a lot of black build up on my plug, I should be good correct?