Anyone know how to adjust springs on CVT?

[BeaverRat]

Hello,
I noticed that my CVT/99cc predator build is not picking up speed very well. It accelerates like a bat outta ****, but only reaches a top speed of 30 mph. I checked the ratios, and they indicate that the top speed should be 42 mph at 5500 RPM's (in high ratio on the CVT) and this is RPM's which I know this engine is capable of. Anyway, the issue is that the engine is not even getting up into the high rpm's. It seems to accelerate and then just stop increasing in rpm when it hits 30 mph staying at roughly 3600-3800 RPM. What is causing this issue? I noticed that the CVT switches into high ratio very quickly, and was wondering if I could somehow adjust the springs to force it to stay in low ratio for a longer time (so the RPM's can build up). This way it would switch into high when the engine rpm's are already high.
Thanks

Here is some more info about the bike...

http://motorbicycling.com/showthread.php?t=39424

 

[Goat Herder]

Check with Scotto I think he has these all figured out and is about a Master with them. Might P.M. him? http://motorbicycling.com/member.php?u=21097

 

[wayne z]

Sounds like your overall ratio may be too tall for the engine. Ditto on checking with Scotto

 

[BeaverRat]

Sounds like your overall ratio may be too tall for the engine. Ditto on checking with Scotto

No... I dont think so. The ratio in high is 10.4:1. This is the same ratio I ran with the AGK build and it reached top speeds of 42 with ease. I am wondering if this is from drag caused by the CVT belt system itself. But that would not make sense as it just cannot seem to get above 3800 rpms, but screams up to 3800 with ease. The acceleration from 0-30 is pretty insane.

 

[wayne z]

No... I dont think so. The ratio in high is 10.4:1. This is the same ratio I ran with the AGK build and it reached top speeds of 42 with ease. I am wondering if this is from drag caused by the CVT belt system itself. But that would not make sense as it just cannot seem to get above 3800 rpms, but screams up to 3800 with ease. The acceleration from 0-30 is pretty insane.

Do you have a jackshaft reduction after the CVT? It's my understanding that if you don't, and your final belt or sprocket isn't about the size of the rim, then the gear ratio is gonna be way too tall to get full useable range outta the CVT.
Hope I ain't preachin' to the choir LOL

 

[wayne z]

3800 at 30 mph is a lot taller than10.4. I'm guessing that's around 8:1 without checking the gear calculator.
My Preddy is at 10.8:1 and I'm turning 4200 at 30 mph.

 

[BeaverRat]

Do you have a jackshaft reduction after the CVT? It's my understanding that if you don't, and your final belt or sprocket isn't about the size of the rim, then the gear ratio is gonna be way too tall to get full useable range outta the CVT.
Hope I ain't preachin' to the choir LOL

Yes, I do have a jack shaft reduction after the CVT. It goes as follows:

11 tooth output of CVT to 26 tooth input on jack shaft, 9 tooth output on jack shaft to 44 tooth input on wheel. This provides a ration of 11.556:1. When the CVT is in high it achieves a ration of 0.90:1. Thus in high on the CVT, the final ratio is 0.90*11.556 = 10.4:1.

3800 at 30 mph is a lot taller than10.4. I'm guessing that's around 8:1 without checking the gear calculator.
My Preddy is at 10.8:1 and I'm turning 4200 at 30 mph.

No, 8:1 at 3800 rpm with a 26" wheel would put you at 37 mph. The RPM's are in the ballpark of 3800-4000 RPM when I am traveling at 29 +- 1 mph.

 

[Ibedayank]

beaverrat

take and post a link of your throttle linkage for us showing the recoil side of the motor

sounds like to me the governor is still hooked up and working

that will limit it to 3600-3800 rpm

 

[BeaverRat]

beaverrat

take and post a link of your throttle linkage for us showing the recoil side of the motor

sounds like to me the governor is still hooked up and working

that will limit it to 3600-3800 rpm

Governor is definitely not hooked up. I have done this exact build before with a AGK jacks-shaft for a friend so I basically know what I am doing... It will rev over 5000 if the back wheel is propped off the ground, but not when it is actually running on flat.

I was very thorough before posting here, so I'm pretty sure the answer is not going to be an obvious one.
Thanks though - keep the input coming!

 

[agk]

Those CVT's seem to drag the engine down on the top end. We built a 200cc engine that could turn over 7500 rpm. With the CVT attached we had a real hard time reaching 5000 rpm. There seem to be two reasons for this. One, the CVT would transfer from low gear to high gear too quickly. This would appear to put a heavy load on the engine and prevent it from reving into the higher rpm. Second, high gear on the CVT is just too high to allow the engine to get into the high rpm range.

The first thing we did is try every spring position for the driven spring. We actually felt very little difference between the three positions. Next we installed a stiffer yellow spring on the driven sheave. The idea is with a stiffer spring the CVT will transition slower from low gear to high hear allowing the engine to get into its powerband. The yellow spring helped a little and we were able to pick up a few more rpm.

Then we played with gear ratio. We figured if the engine would not rev over 5000 rpm we'll just gear it lower. We picked up some rpm but surprisingly reached a point with the gearing where the bike was getting slower with the low gearing so we had to take it back to where we were getting the most rpm and mph.

In the end we couldn't get any where near 7500 rpm with the CVT. I know you're using a 99cc engine and maybe looking for about 5000 rpm with your setup. I think you are running into the same issue we had where the CVT has drag from the belt and a high enough gear ratio that will not allow the engine to reach its rpm potential. The bottom end is stellar with the CVT's low gear ratio. That excitement quickly fades in the quick transition from low to high gear.

At the track Scotto was always a step ahead of us with his CVT setup. Maybe he'll chime in with more information. At this point our opinion of the CVT is its great for low end torque and is a great setup for a decent cruising speed. However it does not compare to a single speed jackshaft for top end performance. And even if we could get it to turn close to 7500 rpm we would just tear up the belt. We shredded several belts while doing our R&D on the CVT. Will your 99cc pull big wheelies with the CVT like the 200cc bikes do?

 

[BeaverRat]

Those CVT's seem to drag the engine down on the top end. We built a 200cc engine that could turn over 7500 rpm. With the CVT attached we had a real hard time reaching 5000 rpm. There seem to be two reasons for this. One, the CVT would transfer from low gear to high gear too quickly. This would appear to put a heavy load on the engine and prevent it from reving into the higher rpm. Second, high gear on the CVT is just too high to allow the engine to get into the high rpm range.

The first thing we did is try every spring position for the driven spring. We actually felt very little difference between the three positions. Next we installed a stiffer yellow spring on the driven sheave. The idea is with a stiffer spring the CVT will transition slower from low gear to high hear allowing the engine to get into its powerband. The yellow spring helped a little and we were able to pick up a few more rpm.

Then we played with gear ratio. We figured if the engine would not rev over 5000 rpm we'll just gear it lower. We picked up some rpm but surprisingly reached a point with the gearing where the bike was getting slower with the low gearing so we had to take it back to where we were getting the most rpm and mph.

In the end we couldn't get any where near 7500 rpm with the CVT. I know you're using a 99cc engine and maybe looking for about 5000 rpm with your setup. I think you are running into the same issue we had where the CVT has drag from the belt and a high enough gear ratio that will not allow the engine to reach its rpm potential. The bottom end is stellar with the CVT's low gear ratio. That excitement quickly fades in the quick transition from low to high gear.

At the track Scotto was always a step ahead of us with his CVT setup. Maybe he'll chime in with more information. At this point our opinion of the CVT is its great for low end torque and is a great setup for a decent cruising speed. However it does not compare to a single speed jackshaft for top end performance. And even if we could get it to turn close to 7500 rpm we would just tear up the belt. We shredded several belts while doing our R&D on the CVT. Will your 99cc pull big wheelies with the CVT like the 200cc bikes do?

Excellent info! Thanks for writing that all up.

May I ask where you bought the stiffer spring for the driven pulley? I think I will try that out, as right now it is almost immediately jumping into high gear - way too soon.

Yes, if I'm leaning back, it will definitely fly pop a wheelie! Incredible low end torque...

 

[agk]

BMI sells the yellow driven spring and I believe we also purchased one from Comet Kart Sales. They also sell stiffer springs for the clutch. The stock clutch springs failed in a short amount of time. We replaced them with stiffer clutch springs which provided an approximately 3100 rpm engagement. We liked the higher engagement better since these little engines idle so high.

Just as a note, we also experimented with some spacers on the shaft of the driven sheave. The idea was to install a spacer that would limit how far the driven sheave could open. We thought we could prevent the CVT from going all the way into high gear and be able to build more engine rpm. We had three different spacers made in three different thicknesses. We failed to increase our top speed with this idea.

With the 200cc engine linked to the CVT our best top speed was 47 mph. This was with the stiffer clutch springs and the yellow driven spring. Not much better than the 45mph we were able to achieve with the CVT completely stock out of the box. Just a little background on what we've done so far to fine tune the CVT.

 

[calvynandhobbs]

This is great info since I have a 99cc Pred and CVT in boxes in the garage. Maybe I'll just have to go with jackshaft and clutch set up for this build and save the CVT for another build on another day.

 

[BeaverRat]

This is great info since I have a 99cc Pred and CVT in boxes in the garage. Maybe I'll just have to go with jackshaft and clutch set up for this build and save the CVT for another build on another day.

I would have to say at this point to not go with the CVT with a 99cc bike if you are looking for a very fast bike. Here are my observations:

-With the CVT the acceleration and torque are amazing (much better than a jack-shaft). You can go up any hill with ease, and it has an extremely smooth start.

-Downside is that the top speed with the stock springs will be about 30 mph on flat ground no matter what your gear ratio is. This is with the proper gear ratio setup. If you are geared too high it will bog, and if you gear too low, you will be limited by the max RPM's of the engine. I have found the perfect ratio with the 99cc and CVT to be about 10.4:1 in high ratio mode.

-A jack-shaft system (such as AGK's) will allow you to have a much higher top speed. I was able to achieve 42 mph pretty easily with a 10.4:1 fixed ratio. You will of course have worse acceleration, but it will still be miles above that of the china girl 49cc 4 stroke engine.

 

[calvynandhobbs]

I may dig a little more info up on the Q-matic with the 99cc Predator. I've seen a couple posts where they are able to allow the engine to spin up like it's supposed to. We'll see. I'm in no hurry at this point and have too many honey-do projects going on to even think about starting it for a little while.

 

[donphantasmo]

You know what I just thought about??

Check on the Polaris forum. Polaris 4x4s have a CVT transmission. I went to Youtube and looked at a guy changing the springs on the Transmission.

here is one

here is another

This might be too advanced for our little bikes. But this should give you the knowledge to see what and how they work.

Hope this helps

 

[scotto-]

Those CVT's seem to drag the engine down on the top end. We built a 200cc engine that could turn over 7500 rpm. With the CVT attached we had a real hard time reaching 5000 rpm. There seem to be two reasons for this. One, the CVT would transfer from low gear to high gear too quickly. This would appear to put a heavy load on the engine and prevent it from reving into the higher rpm. Second, high gear on the CVT is just too high to allow the engine to get into the high rpm range.

The first thing we did is try every spring position for the driven spring. We actually felt very little difference between the three positions. Next we installed a stiffer yellow spring on the driven sheave. The idea is with a stiffer spring the CVT will transition slower from low gear to high hear allowing the engine to get into its powerband. The yellow spring helped a little and we were able to pick up a few more rpm.

Then we played with gear ratio. We figured if the engine would not rev over 5000 rpm we'll just gear it lower. We picked up some rpm but surprisingly reached a point with the gearing where the bike was getting slower with the low gearing so we had to take it back to where we were getting the most rpm and mph.

In the end we couldn't get any where near 7500 rpm with the CVT. I know you're using a 99cc engine and maybe looking for about 5000 rpm with your setup. I think you are running into the same issue we had where the CVT has drag from the belt and a high enough gear ratio that will not allow the engine to reach its rpm potential. The bottom end is stellar with the CVT's low gear ratio. That excitement quickly fades in the quick transition from low to high gear.

At the track Scotto was always a step ahead of us with his CVT setup. Maybe he'll chime in with more information. At this point our opinion of the CVT is its great for low end torque and is a great setup for a decent cruising speed. However it does not compare to a single speed jackshaft for top end performance. And even if we could get it to turn close to 7500 rpm we would just tear up the belt. We shredded several belts while doing our R&D on the CVT. Will your 99cc pull big wheelies with the CVT like the 200cc bikes do?

I think everything AGK mentioned here pretty much sums it up. The CVT has great power transfer from 0-30mph and then pulls strong to whatever RPM your set-up (gearing) will allow. You can't beat a CVT off the line to the first turn, but it does rob your engine of the upper rpm range that it could normally attain.

With this in mind I've found it better to run a lower gear ratio which will give you higher revs overall and great bottom to mid-range power, but you will still be suffering on your total top speed even with it's overdrive ratio.

If you're running on a really short, tight track......you won't beat a CVT set-up with the proper gearing. I am finding that the stiffest springs work best for my CVT set-up, but the stiff springs have been breaking and are very brittle as of late. Also as AGK said, high rpm reeks havok on the belts.....I've gone though my fair share, believe me.

scotto-

 

[N057828]

http://www.ebay.com/itm/49cc-X1-X2-...Parts_Accessories&hash=item256bf4527e&vxp=mtr
Is this the cvt, does it fit I think it should 142f Hua Sheng? But I have a 415 chain so sprocket like to know what type of sprocket to fit it on tranny to drive 415 chain???