What could be causing my acceleration issues?

by Kevin
(Portland, Oregon)

Changed my drive belt after it wore out and snapped. My new belt performance is crap. I use my scooter for everyday commuting in Portland, OR. I know I have the correct belt for my scooter.

I even went to a dealer and bought a different brand belt and tried that one to no avail. I have a 139 QMB Honda rip-off engine with 10 inch wheels so I use the 669-18-30 belt.

I have a Jonway 50CC, 4 stroke Chinese scooter. Despite their lack of quality (I already know this, helpful comments please), my bike had more low end acceleration and a faster higher RPM climb to 30 mph with an old worn out belt than the new one does.

So here is what is specifically different. With my new belt on, my bike pulls away from a stop with the same decent acceleration as it did minutes before it broke. The RPM's climb at the same rate as they always did.

Then when my bike is at around 15-20 mph, the RPM's drop and/or begin to climb very slowly. My scooter now moves extremely slow from 20-30 mph. (this can take like 25 seconds on a flat) Also, my bike's top speed has changed.

On the same stretches of flat road where my bike easily did 40 mph with a specific higher RPM sound, it now goes 30 with a lower engine RPM. Climbing hills that I used to take easily at 30mph, I now do at 20 mph.

My bike sat for only a week from the time the belt broke to the time I put the new one on. My bike has nothing modified since the belt broke (except new roller weights which had no noticeable change) and the performance went out the window.

Any ideas? I put my first 1800 miles on my scooter before the belt broke while scooting. I figured I would just change the belt at like 3000 miles since they can last up to 8000. I learned my lesson.

I guess I ride pretty hard, the hills I climb probably also help to wear out the belt sooner.

What I've already done to try to fix this problem:

• I have taken the entire CVT transmission apart piece by piece and cleaned it all up. There were belt fragments wedged in the pulleys
  and belt powder everywhere.
• I tried putting some new roller weights in which are 6.5 grams. No change. My old rollers were not that bad, around same weight (worn) with no flat spots and could still roll fine in the variator.
• I have thoroughly cleaned the carb out and the airbox.
• I've tightened and checked to makes sure all my hoses are in good shape and seated properly.
• My spark plug looked great. I use an iridium NGK plug. The gap meets the recommended spec of between 0.6 and 0.7 mm.
• Tire inflation is at normal and always has been kept there with no change.

I recently took apart my centrifugal clutch (the driven pulley) to make sure it was clean and functioning properly. The large spring is fine as well as the small springs that hold the pivoting weights back. I cleaned this thoroughly.

I did notice that the pulley rotates and slides out as you pull it against the large main spring, which would allow the drive belt to ride lower at where you achieve your higher speeds. (My problems are in obtaining higher speeds and dealing with a power drop at 20 mph and up so I think this could be something...)

When I pull on the pulley, it slides out but seems stiff, even without the spring and doesn't seem to want to open up all the way, sometimes. There is no way for me to take this apart more so I just put some white lithium on the shaft, opposite of where the belt rides, and worked it in.

The pulley seems to move better, but still gets hung up about 3/4 of the way out in an in consistent fashion. I never took this piece off before my problem so I don't know if this could be the cause. The shaft where the belt rides on the driven pulley seems to be getting slightly greasy as if the rubber bushings at the bottom notches on the pulley may be failing?

I have noticed some minimal slippage while riding and can easily differentiate this slip from the overall lack of performance.

Are they related issues?

If any one has an ideas or knows of a few more simple things to troubleshoot, please pass it along. I'll give them a try and get back to you.

Thanks for any help in advance.