Heavy "clunk" in gearbox area

[kiwiz]

Hi,

My old J has been making some heavy " clunking" sounds when it is declutched at low speeds so as to avoid a stall and when clutching again to resume progess. its quite a deep clunk,

I have managed to emulate this by running the bike in low gear on the mainstand. firstly when declutched but in low gear there seems to be significant friction such that application of the rear brake or a very heavy grip with hands is required to stop rear wheel rotation. I assumed that this was just normal friction in the wet clutch. Rolling the throttle on and off slightly with it in low gear whilst clutching and declutching seems to provoke the same heavy "cluncking" noise.

Could it be as simple as just rear chain tension or something more sinister? I have eyeballed the rear chain and that looks fine and earlier I had a lot of problems with the declutching lever over rotating and jamming declutched until I discovered the the Clymer manual only dealt with the worm adjuster and that my ball and ramp system adjustment mechanism was done 100% the reverse!

Bike runs fine under load and clutch seems to operate correctly under normal road conditions. Anything to worry about?