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

Discussion in 'Transmission / Drivetrain' started by rjriggs, Sep 21, 2015.

  1. rjriggs

    rjriggs Member

    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?
     

  2. jaguar

    jaguar Well-Known Member

    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.
     
  3. rjriggs

    rjriggs Member

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

    crassius Well-Known Member

    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
     
  5. rjriggs

    rjriggs Member

    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?
     
  6. butre

    butre Well-Known Member

    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.
     
  7. crassius

    crassius Well-Known Member

    what he said
     
  8. jaguar

    jaguar Well-Known Member

    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.
     
  9. rjriggs

    rjriggs Member

    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?
     
  10. jaguar

    jaguar Well-Known Member

    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
     
  11. crassius

    crassius Well-Known Member

    don't know what intake you have or what carb, but an NT style carb has 4 slots for gripping the intake - there should be a flat surface inside carb that the intake should be right onto when it is right - if steel intake, sometimes there is a bit of chrome sticking up at end, file this smooth to get carb all the way on
     
  12. rjriggs

    rjriggs Member

    Okay. I took my bike out on a long, flat stretch outside of my neighbourhood, which is where I've done all of my testing so far, and it seems to be working fine. With a little pedalling, I got it up to 31 mph, after which it maintained that speed on its own. So I guess I've been expecting it to have more acceleration than it has. Oh, yeah...after that ride I noticed my idle screw was gone! Unrelated to the improved performance, I assume?
     
  13. crassius

    crassius Well-Known Member

    might even have slowed you down a bit - takes some filing to get a nice, small, smooth end on one so the slide doesn't get pushed in, but not all that hard to make one
     
  14. butre

    butre Well-Known Member

    nt idle screws are notorious for vibrating out. a little blue loctite or a piece of fishing line in the thread will prevent that
     
  15. rjriggs

    rjriggs Member

    What about getting a longer screw with a hex nut on it, adjusting the idle screw until it's where it needs to be, and then screwing the hex nut up against the engine?
     
  16. mikedabomb

    mikedabomb Member

    Top speed is not closely tied to the weight of a rider. Acceleration, on the other hand, is. More weight=takes longer to reach top speed, however top speed would not be affected much as only problems are tire and bearing squish. Slipping clutch would sound like the engine is rapidly gaining rpms without acceleration, and then holding those rpms but slowly increasing speed.
     
  17. nishikidrift

    nishikidrift Member

    wascowee wabbit...
     
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