Yanmar 1GM Question

[Thomas Dunne]

I have a 1982 27 Hunter and I'm the original owner. My 1GM Yanmar runs well but I experience a 300 - 400 rpm flucuation in the engine rpms when running along. I'll set the throttle to say 3000 rpm and as I cruise along the engine will drop to 2600 - 2700 and then run up to 3000 or so without any change in the throttle setting. I've checked the linkage and it looks and feels OK to me. Any help would be greatly apprecitated as this is the only problem I've been unable to diagnose and resolve.

 

[Jay Kent]

I had that same issue with mine

last Fall. Eventually, it dropped clear down to 2000 RPM, and tended to stay there. The injector was pulled, sent out and re-installed. I have had no issue with that since.

 

[Mark Wilson]

Yanmar 1

Thomas, It sounds like a fuel pick up problem. Check all the fuel lines for cracks and tightness on the fittings. If that don't fix it try replacing the fuel lines. Also, make sure you have enough fuel in the tank.

 

[Steve Dion]

Try the cheap way out first.

Thomas:I would try Marks way first. Pull the fuel pickup tube out of your fuel tank and check the end of the tube. If there is still a screen on the tube, you may either want to remove it completely or clean it and reinstall. If the screen is not plugged and the fuel tank is clean then look at the injector cleaning.I do not think that injector cleaner is going to do you much good if the injector is crapped up. These additives seem to do better as preventative maintenance. Before you have your injector cleaned, find out how much it is for a new/rebuilt one. Sometimes the prices will surprise you.

 

[David]

Surge

Have you checked the engine mounted fuel filter? I had the same surge problem and it was a small particle of dirt that kept lifting and then releasing.

 

[Gunter Meyer]

fuel pump

My 1GM rpm began oscillating when somehow therubber gasket under one of the jets in the fuel lift pump split. If nothing else does the trickthink of the fuel pump output pressure.