[scooder]

Flatjack, I see your point re the brake piston, I makes sence, I think that the piston doesn't completely lift of the plate except on the over run. I've seen with the piston removed, the timing flicking about when using a timing light. With the piston in, at idle the timing stabilised.
Wether they all do this, I don't know, but the one I seen did just this.
Mr topless, you got some things to look at an try, do report back your findings.
Martin.