View Full Version : Fluctuating RPM Yanmar 3GM

Daniel Daoust
11-08-2007, 09:44 AM
"I own a Yanmar 3GM 700 hours. Oil and filter changed every 100 hours. For the first time at end of season while running at 2000RPM the engine suddenly went down to 1200 rpm, increasing the fuel throttle would not do anything except having it to lower even more (sensing it would die).

I then proceeded at decreasing the fuel input (throttle) for a while ( 5 minutes) then when i throttled it back up and it ran fine again.

This scenario happened a couple of times so far.

Any Idea?


11-08-2007, 02:01 PM
check for fuel restrictions. fuel pickup screen plugged? (In tank) tank vent plugged?

11-08-2007, 08:02 PM
"Hi Dan, sounds as if you are sucking in air from fuel feed pump & on. Check that. You should be running that enhine at 3000 rpm. Max will be 3600. At 3000 you get max torque and min fuel consumption. Yanmar designed this engine to cruise all day at that rpm. Running it lower will cause to light a load. Diesels have to work to be efficient."