hmmm, CVT performs best with worn belt!

[308reticle]

Hey folks,

First and foremost, I have been lurking around as a guest for a week or so and finally decided to stop being a leech and join up already!   From what I can tell, you all look to be a good group of helpful forum members.  

So back to task at hand.  Backstory:  I scored a free 2009 VIP Future Champion 49cc gy6 that was laying around my friends farm accross the street from me.  He got it for free so I dont know much about its past. From what I can tell, its been laid down more than once. And Im assuming it was someones DUI mobile.  Maintenance looks to be slim to none.  So after telling myself over and over not to go crazy and spend too much money on this haggard old scoot, I decided to keep it simple.  I ordered a cheap "performance" kit from J and J Powersports. It came with  "Precision Jetted Super-flow carb, High Performance Coil & CDI for increased spark and engine timing, and
Super Flow Air Filter."  Their words not mine.  Also got a  belt and 7 gram rollers for free.  When the parts showed up it was clear to me that i just got suckered. The parts received weren't the parts in the picture. However, It did wake the little 49cc motor up a bit.    

So after getting everything working well, it was time to tackle the CVT.  Now CVTs and I have a love hate relationship.  Im familiar with them due to modding a few Polaris RZRs over the past few years.  Currently still battling to get my clutching tuned right on my RZR XP turbo.  So while I understand the concept, im man enough to admit that my patience with CVT systems are lacking and I usually end up bruised beaten and defeated.

I pull the cover only to find what i expected to find.  a mess.  after inspection i found that i need a new primary (i believe its called a variator in the scooter world?)  the sheaves look like they chewed up a bolt or something at one point. But for now all i have is a new cheapo secondary to put on and some new weights and belt.  

Heres where it gets interesting.  Comparing gates belt I pulled off and new knock off belt I got for free, it was clear the new belt was wider.  Witch I expected because the old gates belt was clearly worn hard. (should have seen the amount of belt dust in case)  so first thing I did was put on new belt and run it. with new belt it would not run out well. it just sat down around 5k rpm and didnt really want to get up and go. so i messed with weights and got a little more acceleration but still lacking in rpm range (shooting for around 8k rpm)  so finally I put in new secondary springs. (blue).  

after changing around weights and springs I still had the same problem. lacking hard in top speed and barely catching 6500rpm downhill.  So finally I ended up with this:  New (cheap) secondary with blue springs in it,  factory weights in primary, and old worn gates belt.  For whatever reason that old belt gets it running the best.  great acceleration. still a little lacking in rpm but during acceleration i see about 7k rpm.  but once the belt runs out  my revs will drop to about 6k then begin to climb up to 7500 on flats and 8 to 8500 on downhill.  

Im not sure where to go next.  Im going to order a new variator because mine is pretty beat but why in the world does my old worn out belt make this thing go and the new belt leaves me feeling like it would be faster to get off and walk?

[pinkscoot]

CVT's are the great mystery of scooters. A lot is trial and error, with some magic involved. Is the belt the same size as the original one was when it was new. It should be the same length width and angle. Maybe someone here with a Chinese 4 stroke can help with that. How far down on the variator is the new belt sitting? Is the new belt using all of the variator? Mark it with a sharpie and do a run and see if the new belt is getting full travel. Its possible that its traveling all the way out faster so you run out of variator before you get the engine speed where you want it. keep us posted on how its going.

[GrumpyUnk]

A new belt is wider(perhaps shorter, also). A wider belt will tend to bias the gearing. The spring will tend to push/pull the belt towards 'low' gear as it tries to move, and the variator pulley will essentially be in a higher gear at a given rpm with a new belt, as it won't fit as easily between the two halves of the variator pulley. IOW, they fight. When the variator is totally relaxed, and the spring is totally expanded, you are in the lowest gear you can get. Add some rpms, and the variator starts to grab, tighten the belt, and continue as the rpms increase. The clutch will do nothing(no grab) until x,xxx rpm is reached. Once it gets there, the clutch will start to transfer power(however much the variator/spring contest has determined) to the output gearbox. If you use high rpm clutch springs, nothing will happen until rpms are up there, at which time, the variator and spring may have already decided who will win their tug-o-war. (might be in 'high' gear if the rpms are high enough. The variator and spring know bupkis about the clutch engagement.
Most clutch springs don't take things that far, and the clutch starts to engage while the variator is still in lower gear position. As the rpms go up, the variator will squeeze together(wider belt == squeeze sooner), and upshift the ratio. Narrower belt, and the variator won't squeeze so much until it is at higher rpms, I think. I'm sure the experts will chime in with more.
tom

[snaker]

I haven't had the opportunity to see a RZR CVT so I don't know what you have there. (Pictures please?). I have quite a bit of experience with snowmobile CVT's, mostly Polaris P85 systems and some Team secondary's. That is predominately in maintenance, not modding . You can get manuals and charts/ part lists thru Polaris on basic CVT tuning. Not so much with these GY6 styles.
Based on the P85 to compare to the GY6 type you have:
Both use a RPM sensing (flyweights/centrifugal force) drive pulley and a torque sensing (slots/ramps) driven pulley.
Beyond that there's not much in common.
The P85 clutching function is in the drive pulley using a "contra spring" to force the sheaves apart wider than the belt, that's the clutch. That spring also teams up with the driven contra spring(the big single spring) to oppose the fly weights.
The GY6 has an actual clutch mounted on the driven pulley, similar to a chainsaw clutch(that has the three small springs).
The big noticeable difference is that on the P58 the belt is not moving when the engine speed is below engagement rpm. The GY6 style has the belt moving anytime the engine is running.
The big CVT parts are crazy expensive and people tend to follow others advice and experience for modding. The china stuff is cheap enough to allow someone to try a lot of different stuff.
Last thing, I my opinion these GY6 CVT's require regular maintenance or they just fall apart.

[tortoise2]

Jun 28, 2018 23:07:17 GMT -5 308reticle said:

2009 VIP Future Champion 49cc gy6 . . old belt gets it running the best

If a 10" rear wheel and a 669 belt . . potentially related discussion.

[snaker]

Had to take a break, my keyboard was getting tired. To your issue.
A couple times you mentioned blue springs. Not sure if typo or not but the three springs are clutch related (engage/disengage). The single big spring affects the shifting.
Also with the belt width. At a specific rpm a narrow belt will ride lower in the drive pulley which will cause it to stay higher in the driven pulley resulting in a "lower gear"
Your description sounds like the CVT had been retuned for the skinny belt and now with the wider belt it needs to be retuned again.

[308reticle]

thanks for the response guys. sorry for being MIA directly after posting but I was actually up in Northern Maine riding with my RZR. And naturally, I shredded another belt. So I think its safe to say cvt systems in any form of motorized vehicle hate me haha!

Anyway, The blue springs I spoke of were labled 1000 rpm springs. it came with the clutch springs and the contra spring. (3 small and 1 large) Since I have a 50cc with minimal modding i figured it would be best to stay closer to stock spring weights. I had hopes the heavier blue spring would help me on the hills. I have alot of them around the area. after reading torise thread link, im beginning to suspect i have a knock off belt. it has the right numbers on it and the overall length looks to be correct but I have never heard of the brand. "FANG-XING VS BELT" 669 18 30 C146 17 L7. Like I said, It was free with my order of that "performance kit" So if its out of spec that would make sense as to why any configuration I throw at it doesnt seem to help. What seem to be the best belts for the short cases? I think I may start there and see if i see any change. at the very least I will at least be able to take the bad belt possibility out of the equation. I will also mark with a sharpie to find where my belt is riding. I never thought of doing that. such a simple solution! I will report back when I get everything in and test ran