When you select first at a standstill with the engine running, the bike gives a clunk and a small jolt. Some clunk is normal on most motorcycles, especially when cold: the clutch plates still turn the gearbox a little, and the gear engages against that movement. A very loud bang, a lurch forward, or a stall means the clutch is not releasing well, the idle is high, or there is slack somewhere in the drive.
Is it safe to ride?
Yes, usually. If the bike lurches forward when you select first, hold the front brake while you do it until it is fixed.
Quick checks first
- Is it only loud for the first few minutes on a cold morning?
- Pull the clutch lever, wait two or three seconds, then select first. Is it quieter?
- Does the bike creep with the clutch pulled?
- Is the idle faster than usual?
Diagnose it step by step
1Does the clunk get much quieter once the engine is warm, or when you wait a moment after pulling the lever?
- Yes: this is mostly normal. Cold oil holds the plates together. Use the grade in your manual and wait a moment before selecting first.
- No: go to step 2.
2Does the bike creep or try to stall when you select first with the lever pulled?
- Yes: the clutch is dragging. Adjust clutch lever free play (K-Light 125: 10 to 15 mm); hydraulic clutch: Bleed a hydraulic clutch. Then follow Clutch drags.
- No: go to step 3.
3Is the idle speed higher than specified? (K-Light 125: 1500 ± 100 rpm.)
- Yes: Idle speed is too high.
- No: go to step 4.
4Is the oil old, low or the wrong grade?
- Yes: Check the engine oil level, Change the engine oil.
- No: go to step 5.
5Is there a lot of slack in the drive: a loose chain, worn cush rubbers, or loose engine mounts?
- Yes: Check and adjust chain slack, Check the cush drive rubbers, Check engine mounting bolts.
- No: go to step 6.
6Still a loud clunk with everything above correct?
- Warped steel plates may be dragging. Go to Inspect and replace clutch plates and springs.
Causes, most likely first
| Cause | How to confirm | Fix |
|---|---|---|
| Cold oil (normal) | Quieter when warm | Wait a moment; correct oil grade |
| Clutch drag | Creeps with lever pulled | Adjust clutch lever free play |
| High idle | Revs above specification | Idle speed is too high |
| Slack in the drive | Loose chain, cush play, loose mounts | Check the cush drive rubbers |
| Warped clutch plates | Persists after the above | Inspect and replace clutch plates and springs |
Reference values (K-Light 125)
| Item | Value | Source |
|---|---|---|
| Clutch lever free play | 10 to 15 mm | K-Light 125 manual, PDF p. 69 |
| Idle speed | 1500 ± 100 rpm | K-Light 125 manual, PDF p. 49 |