I noticed when I took my 4 cyl. Yanmar Hunter 42 for a spin yesterday that after staying at cruising speed for 15-20 mins, around 2800 rpm, the engine starting to fail drifting up and down 300-400 rpms. I managed to get back to the marina by keeping the engine at 2500 where it didn't seem to be affected. I just finished putting 14 gallons of fuel in my 70 gallon tank froma Very Reputable marina, but I don't know if that's relavent. I haven't changed the fuel or air filters for a couple years. Any suggestions?
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How much fuel is in the tank?
If you were nearly empty when you bought fuel you could have gotten air in the line. Air is what causes that surge. Bleed it first. Bet you find air.
If you were nearly empty when you bought fuel you could have gotten air in the line. Air is what causes that surge. Bleed it first. Bet you find air.
Replace fuel filter
and drain water separator. Adding fuel into the tank (if mostly empty) can stir up a lot of things includying water. Like Fred says also air can get in the lines. Other than the RPM fluctuations check for exaust smoke. White- water. Bluish- oil. Black - fuel. Black smoke usually in concert with loss of RPM is due to soot in the exaust mixing elbow. Hopefully the filters will do it.
and drain water separator. Adding fuel into the tank (if mostly empty) can stir up a lot of things includying water. Like Fred says also air can get in the lines. Other than the RPM fluctuations check for exaust smoke. White- water. Bluish- oil. Black - fuel. Black smoke usually in concert with loss of RPM is due to soot in the exaust mixing elbow. Hopefully the filters will do it.
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