Thanks for the replies so far. More answers:
Air cleaner was good last time I checked but I will double check for any kind of blockage. From what I could see, the breather tube is clear but I didn't check where it enters the intake, just that gas was coming through the tube from the cranks case.
I will double check throttle linkages but I've messed with these before and pretty sure that's not it.
I checked the tappet clearances 2 years ago, expecting to adjust but they were at spec. Stern gland stays very cool.
Again on hours, I think this engine
has seen light use over its 34 yrs but no meter/guage. I expect more problems from probable periods of underuse. I doubt it has 2000 hrs on it.
I picked up a laser/tachometer to check that the gauge is giving me accurate RPM's - I'll test that this weekend.
I have not cleaned the injectors - is that something requiring professional servicing or do I just pull them myself and...?
As I have said, the problem isn't "bad" but if I can put off engine
disassembly/rebuild, its worth any steps that others have taken. I'll pursue a compression
test after some of the steps listed here, and perhaps the injectors?