Clutch Engine seems to be revving too fast for the speed I'm going

[rjriggs]

At greater than maybe 17 mph, my engine seems to be revving higher and vibrating more than is necessary for the speed it's going. Unfortunately, I've never had a motorized bicycle before, so I don't really have any past experience to compare it to, so I'm not sure. Could my clutch be slipping at high speeds? How can I tell? I'm wondering if this is why I can't seem to get it past around 24-25 mph on a flat surface.

EDIT: Can I improve the grip of the clutch pads by roughening them up a bit with sandpaper or a file? If so, what grain works best?

 

[Deleted member 12676]

the pads work better as they wear down so by roughing them up you will make them worse.
if it is slipping at high rpm then it is slipping at low rpm too
but since you are attaining a normal maximum speed I'd say you're just hallucinating and it's ok.
but yes it does vibrate more at high rpm because the crank is not properly balanced. you have to balance it yourself.

 

[rjriggs]

My kit is an F80 from thatsdax.com. Duane, the owner, claims he hand-balances the crank, but maybe it needs a little adjusting.

 

[crassius]

if you are of normal weight and within a 1/2 mile or so of sea level, you should get about 35mph out of a 44 or 41 tooth rear sprocket - do a search here about how the clutch & cable are to be properly adjusted - excess vibration on a balanced crank almost always means bad motor mounting, though, so I'd check that first

 

[rjriggs]

I weigh around 170-180 lbs,and I've got a pretty heavy beach cruiser bicycle from Walmart. Surely that can't lower the speed by 10 mph! ...can it?

 

[butre]

I weigh 220 and get around 30 out of a stock kit. check motor mounts. if you can grab the engine in one hand and bike in the other you shouldn't be able to move one in relation to the other. just tightening the studs doesn't make a difference either, it only needs about 15 foot pounds. there shouldn't be any gaps anywhere between the motor and frame, if there is you need to shim the rear mount or file either front or rear mount until it fits.

 

[crassius]

what he said

 

[Deleted member 12676]

well according to a recent post DAX has been making claims about his products that aren't true.
If it vibrates too much (so that you can't use the rear view mirror because it vibrates too much) then the crank isn't properly balanced.
I tell on my site how to balance it.

 

[rjriggs]

Okay, I'm goofy. After riding and observing carefully, I don't think the engine is revving too high or vibrating too much. Seems it seemed to be happening when I was clutching the motor while going downhill. I adjusted the idle screw, and that took care of it. Back to the drawing board on why this thing won't go over 25 mph on a flat surface. Now I have on a couple of occasions forgotten to turn off the petcock valve overnight. Can that have something to do with it? Is there something I need to clean out?

Another possible culprit: a potential air leak. Whose idea was it to put those two little grooves where the carb meets the intake manifold? The carb wouldn't go in far enough to completely cover them up, so I put electrical tape over this, but this may not have completely solved the issue. I'm going to try gasket sealant next.

Also, my bike is still all stock parts. I'm going to try replacing the spark plug in a day or two, but surely that won't make all that big a difference, will it?

 

[Deleted member 12676]

there is not hardly a single thing about that engine that can't be modified to make it stronger and faster (and also more reliable).
Welcome to the rabbit hole