You open the throttle, the engine revs high, but the scooter picks up speed slowly, especially from a stop, uphill or with a passenger. In an automatic scooter, a rubber belt carries power between two pulleys, and a centrifugal clutch connects the rear pulley to the wheel. If the belt is worn, oily or glazed, or the clutch shoes or drum are worn, power is lost as slip. The K-Light manual's generic power-loss chart lists clutch slip, belt wear, worn rollers and worn or grooved pulley faces for scooters with this drive. For limits and settings, follow your scooter's manual.
Is it safe to ride?
Ride with care. A slipping belt gets hot and can break without warning, leaving you with no drive in traffic.
Quick checks first
- Is the engine strong? Do the revs rise quickly and cleanly?
- Check the tyre pressures and spin the rear wheel to check the brake is not dragging.
- When was the belt last changed? Check your service record.
- Any squeal or burning rubber smell from the drive case?
Diagnose it step by step
1When you open the throttle, do the revs rise strongly while the speed lags behind?
- Yes: drive slip. Go to step 2.
- No, the revs are slow to rise too: the engine is weak. Go to Engine feels weak and down on power.
2Is a brake dragging or a tyre soft?
- Yes: Check for brake drag, Check tyre pressure.
- No: go to step 3.
3Open the drive case (engine cold). Is there oil or grease on the belt or pulley faces?
- Yes: the oil came from a leaking seal or over-greased parts. Find and fix the leak first (Oil leaking from the scooter rear gear case), clean the faces and fit a new belt.
- No: go to step 4.
4Is the belt cracked, glazed, frayed, or narrower than your manual's minimum width?
- Yes: Inspect and replace the scooter drive belt.
- No: go to step 5.
5Are the rollers flat-spotted or the pulley faces grooved or blue?
- Yes: Check variator rollers and sliders.
- No: go to step 6.
6Still slipping with a good belt and rollers?
- The clutch shoes may be worn or glazed, the drum (bell) worn, or the rear pulley spring weak. Go to Check the scooter clutch and bell.
What happens if you keep riding it: the belt overheats, glazes and breaks, and heat can damage the clutch and pulley faces. See Scooter drive belt has broken.
Causes, most likely first
| Cause | How to confirm | Fix |
|---|---|---|
| Worn or glazed belt | Narrow, cracked, shiny | Inspect and replace the scooter drive belt |
| Oil on belt or faces | Oily case, wet belt | Fix leak; Change scooter final drive oil |
| Worn rollers or grooved faces | Flat rollers, grooves | Check variator rollers and sliders |
| Worn clutch shoes or bell | Belt and rollers good | Check the scooter clutch and bell |
| Dragging brake or soft tyre | Wheel hard to spin | Check for brake drag |