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Old 08-22-2011
yjchun yjchun is offline
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yanmar 3gm30f 1 cylinder bad condition

Hello.

My new (first) boat has a 10 years old yanmar 3gm30f.
Engine works fine but not good sound and vibration (especially in low RPM) and feels like underpowered.
I am planning to bring the boat to my home next month and do not want it stop in the middle of the ocean.
I do know next to nothing about the engine but here (in japan) engine repair/overhaul is very expensive and don't want to hire anyone unless very required.


Symptom:
1. Engine stops at lower than 1100 idle rpm
2. for 1 minute after engine start, white smoke, a little lower rpm, worse sound and vibration than later.
3. bad vibration and sound at idle or low rpm gets a lot better when I engage engine to >2000rpm for a while (10~20 seconds is enough).


Analysis:
1. When I turn the decompression lever ON of cylinder 1, RPM goes up with better sound. So I guess it is problem with cylinder 1
2. Checked fuel is coming out from high compression fuel line (by manually rotating the crankshaft). No knowledge if the fuel amount and timing is OK or not but fuel line is not blocked and fuel pump is working at least.
3. I replaced the injector with cylinder 1's. No change. So injector seemed OK.


This is all I could do myself so far. What are your suggestions from now?

Thanks
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