Stumbles when turned off / Dieseling

[79beem]

Bike has started doing the above.
Is there a reason other than a hot spot in the pot?
What is the remedy.
Valves,points,plugs,timing,carb balance done 2500km ago with no problems.

[Barry]

Once there is no spark any running on can only be due to a hot spot.

How does the carbon build up look through the plug hole ?

Assuming carb settings are correct a good hard run might help otherwise there is the steam cleaning option where you spray a mist of water into the carb intakes while holding the engine at mid revs. Ideally that should be done just before an oil change is due in case the oil gets contaminated. It didn't seem to when I tried it but it's still a sensible precaution.  

[montmil]

Yes, there's a hot spot within the combustion chamber -one or, possibly, both- somewhere that's mimicking the BMW ' built like a tractor' legend.

Are you running spark plugs with an extended nose? Any fuel additives that might be causing buildups of carbon? Is the majority of your riding in town with few lengthy highway romps? Recent change of fuel vendor?

Sometimes, a problem may surface after the last maintenance or adjustment was done.

Perhaps try a tank full of Shell's premium, high caffeine, blend. Hot rod guys say the cleaning agents in that fuel really works for them.

[Armen]

Pop off the top end. Decarbonize. Clean valves and pistons. Cut valve seats. Check piston-to-cylinder clearance. Check cylinder for out-of-round and taper. Hone cylinders and do the ring break-in ritual.

[79beem]

Thanks guys,
Top tip Monte, no more  stumbling after a tank of  premium.