Q. Why does my scooter accelerate slowly from 0 to 5-10MPH?
Slow moving for the first roughly 10MPH or less is most often caused by one or both of two things. Issues with or improper clutch springs and/or your belt may not be in the best position for take-off.
As the rear pulley and clutch rotate, centrifugal force will try to push the clutch shoes outward. Centrifugal force increases with RPM. Eventually the force will be great enough to overcome the tension of the clutch springs trying to hold the shoes in place and cause the pads to contact the inner surface of the clutch bell. The pads will slip a little, until RPM is great enough that the clutch can fully engage with the bell and ultimately drive the rear wheel.
If the clutch springs are too soft they can't hold the clutch shoes away from the bell until RPM is high enough. This will cause poor acceleration or bogging. Many stock scooters may benefit from stiffer clutch springs. Two-strokes with expansion chamber exhausts (tuned pipes) will often lose some low RPM grunt and may require stiffer clutch springs for stronger launches. Stiffer clutch springs are available to increase engagement RPM. Don't go too stiff or you may rev above peak power or in extreme scenarios the clutch may fail to engage altogether. Ideally the clutch should engage a bit below peak power, other than perhaps in finely tuned CVTs that can remain at peak power nearly at all times. The clutch should engage before the rest of the CVT begins working/shifting so you make use of your CVT's best "1st gear" ratio.
If the variator squeezes the belt when at rest/idle, it may push it up a little in the front pulley and then it has to move down in the rear pulley a little because of typical belt lengths. You have the best take-off ratio when the belt is all the way to the center of the variator, riding on the drive boss, and to the outer edge of the rear pulley. The other ill effect of having the belt squeezed to make a different ratio at launch is that the higher ratio spins the clutch faster than normal, making it act as if you have softer clutch springs so you not only get a less than ideal "1st gear", but also lower clutch engagement RPM.
Wear or damage to clutch parts may also cause slow starts. Sometimes the holes in clutch shoes wear and become elongated over time, allowing springs to fit with less tension. This has a similar effect to using a very soft spring, lowering engagement RPM, and the clutch or at least it's shoes should be replaced. If the clutch bell or the clutch become glazed or worn you may experience clutch slip, which results in elevated RPM while the clutch tries to engage. Glazed components may be able to be deglazed with sandpaper or emery cloth and then cleaned with brake parts cleaner. Belt slip can also increase RPM at launch and may be caused by a belt worn thin or glazed or issues with pulley drive faces.
Related Info :
Clutch Spring Comaparison And Info
Clutch Modifications And Upgrades
Installing Clutch Springs
Lightening The Stock Clutch For Later Engagement
CVT Assembly And Disassembly
<< Back to the Scoot F.A.Q.