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Yanmar 3YM20 problem
Hoping somebody may have some answers/suggestions to problem I have just started experiencing with my 2006 Yanmar 3YM20 (300hrs)
Engine has just started blowing black sooty smoke at 2400 revs. Will not rev out past 2800 revs in forward gear. Thought at first this may have been due to a fouled prop, so hauled boat to check and clean. No fouling present.
Engine will rev out in neutral to max revs (with a little puff of dark smoke for an instant before clearing at 3200 revs) and will rev out to 3000 revs in reverse before black smoke. Engine starts first go, runs smoothly and normally up to the problem revs. Everything else appears normal (i.e temp, oil level and colour etc, air filter is completely clean)
I have discounted over-propping issue as I have a three blade fixed prop that has been on the boat for over a year before I experience the smoke issue and has always ran normally. Engine/shaft Alignment is perfect, Filters have been checked/replaced, tank appears clean and has always been treated when filled.
Could this be a clogged exaust elbow issue, or more likely injector, injector pump or lift pump problem?
any thoughts would be appreciated