Belt Vibration

[sambones80]

The belt on my CPI GTR 50 seems to be shaking and vibrating at higher speeds. It starts to make a humming noise in the 40 to 50 mph range and when I hit 48 to 50 mph all hell breaks loose. It vibrates the whole bike like crazy and makes a very loud hum.

I noticed the belt was rubbing the inside of the CVT cover because it left a black line on it so I went for a ride with the cover off and the noise was different but it still shook a lot when I hit 50 mph. I notice at idle the belt shakes like theres too much slack or something but I've got the red Malossi contra spring and the belt seems pretty tight.

I've replaced almost all of the moving parts except the clutch and TD and I'm running it at rather high RPM's to get into the power band of this engine. Could the problem just be that I need a better torque driver?

CPI GTR 50
Stage6 Racing 70cc kit
Tecnigas Next R
Arreche 19mm w/ modified stock air box
Motoforce racing crankshaft, Motoforce bearings
Naraku Variator w/ 2.7g rollers, red Malossi contra spring

[90GTVert]

:welcome:

It's pretty normal for the belt to shake or seem loose at idle. Some evidence of belt contact on the inside of the CVT cover isn't unusual either. I think all of mine do that. I sanded one cover down so there was no more contact. Didn't really change anything that I could tell.

I'm wondering if perhaps you could have a wheel/tire out of balance. That will often cause a vibration that happens at the same speed every time. It's very common with stock tires, and still can happen with aftermarket tires.

[sambones80]

I really think its coming from the belt. The noise changed quite a bit when I rode it without the CVT cover and I also tried a different belt and it changed a little. Its a high frequency vibration not so much a shake. I've never experienced it on a bike but I have driven cars with out-of-balance tires and other shaky wheel issues and this feels totally different.

[90GTVert]

Have you tried running it up on the center stand with no CVT cover so you can watch it?

[fickertravis]

Do you have the bearing that is inside the cvt cover and rides on the clutch installed? Do you still have the cvt dowel pins in the cvt cover? I once forgot to install the bearing that rides in the cover and experienced the same issues. Significant vibration at around 40-50mph.