Nels,
primarily over-advanced timing, although a lean mixture, plugs too hot, etc. will also play their part in causing detonation.
@ ipgo,
when there's as much carbon on the piston crown and on the cylinder head as in the attached photograph, that will cause detonation or even pre-ignition and 'running on', since the carbon will act as a glow plug.
Not one of mine, btw, just another of those little jobs of clearing up the mess made by someone else...
Nelsthebass wrote:
Sounds like they have been rethreaded at some time - cant think that oil starvation will cause pinking - overheating and seized valves etc maybe - but pinking is usually caused either by poor carburation or timing is it not?
piston with heavy coating of carbon by slcchassis, on Flickr