Thanks everyone for the advice.
Went out last weekend - ran for c. 5 hours Sat & 3vhours Sun - mix of idle / low revs (in river) and c. 80% WOT - 4000 revs,18Kts with no real problems.
Engine is still ocassionally missing a beat - can hear this, but is no longer cutting out.
I think int's a sticky injector, but intend to keep running with some degerent in the mix unless anyone thinks it is really worth stripping the injector out. I'm not sure how it could be better cleaned by stripping it out.
Anyway,thanks as always for the experet advice & views.