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Yanmar 2GM20F RPM issue
Hi, After two weeks of trying to figure this one out I am out of ideas, and need help. (sorry for the long post)
I have a 1987 2GM20F on my new to me sailboat with probably 1500 to 1700 hours on it. After working great for almost four weeks, 2 weeks ago it started to develop a problem that I cannot figure out what it is (neither the mechanic apparently).
The engine starts and idles great, no issues at all, no smoke, nothing. In Neutral, RPMs hit 3700-3800 with the throttle full.
Now the problem, in gear, the engine runs great between 800 and 2400 RPM, after that, I can push the throttle for another inch and nothing happens, then it jumps to 2900-3000 and that is the max it gets with full throttle. A little bit of black smoke (very little) when it hits that high RPM.
Boat sat for a year before I got it.
Before commissioning (May this year), we change oil, change oil and fuel filters (both primary and Racor 500) and impeller, and installed a new mixing elbow. Also installed new air filter.
When this issue started to happen I check the fuel filters, they look like new, no water in the Racor filter.
Mechanic came and check everything and said everything looks good. Then when the problem didn't go away, he thought the issue was with the valves and he adjusted them. None of this helped.
The propeller was never fouled during all this time. I dove and checked it myself as well as the shaft, no issues there. Propeller is original, has not been changed.
Today, after the mechanic adjusted the valves, the issue persisted. I decided to give the bottom a clean (I thought it wasn't bad) and after that the engine worked great, no issues at all. We motored for almost 1.5 hours (no wind at all) and all that time it work great, was able to hit max RPM and kept it cruising at a stable 2800 RPM.
Well, after sailing back (wind picked up) I started the engine, lowered the sails and gave it a try to make sure the problem went away, nope, same thing, between 800 and 2500RPM, fine, then push throttle for 1 inch and nothing happened, then a bit more and RPM jumped to 2900-3000 and a bit of black smoke. Why???? why is it intermittent????
Before I continue to spend money with the mechanic, it would be great to hear your suggestions. I am really at a loss here.
Thanks for any advice.
-Tank vent is not clogged
-Stuffing box leaks about 10-15 drops a minutes, keeping the temp about 25 to 30 degrees above water temp (95-100 degrees)
-It is not a problem with the throttle cable, it does the same when disconnected and push it from the engine. BTW the control at the engine moves smooth with or without the cable connected.
-Stop cable goes all the way in, no problem there.
Last edited by cspaniel; 07-02-2011 at 08:31 PM.