Thanks for all the posts.
some got a bit off topic but hey thats how the discussion goes.
Hellosailor, hard or soft hours? Proper maintenance? Bit hard to tell as I've only owned the boat 2 years out of the last 29. Probably a mixed bag; the last owner kept detailed records & probably did a better job than me. The guy before him let the boat go downhill, which probably included the engine.
Valiente, my engine sounds similar to yours, low engine hours, no real problems but an elderly engine. I'm leaning towards your solution however I'm in no rush; I've got 2-3 years to see how the engine runs and make up my mind.
Sailingdog / artbyjody, understand your points about fuel problems. The previous owner had a theory that you never had to change the fuel filter until it clogged up as their are two inline and you switch to the 2nd one when necessary. When I checked the filter the main one was absolutely clogged with gunk and the taps were stuffed so fuel had always been run through both filters regardless whether the taps were opened or closed!
KeelHaulin, I normally run the engine at maximum revs of around 2,100RPM as thats pushing the boat around six knots and thats generally fast enough. The engine specs state maximum revs of 4,000rpm and continous maximum revs of 3,200RPM. I'll try your suggestion and take it up to 3,200 and see whether I get any black smoke.
Danjarch, should of mentioned that some things have already been repaired / replaced. For example, rebuilt starter motor by the previous owner, rebuilt saltwater pump & exhaust manifold by me, etc.
Probably should of also mentioned my plans are to coastal cruise for the next 3-5 years and then look at longer trips after that. Therefore I have the luxury of seeing how the engine performs whilst still fairly close to home. The rebuild / replace decision would be part of the preparation for the longer trips. So far the engine has performed faultlessly, starts no problem and chugs along no worries. Have always warmed up / cooled down, regularly changed oil, etc, etc.