Engine Rebuild Tuning Yanmar 1GM

[Nicholas Ascione]

My 83 hunter 27 has a Yanmar 1GM. It starts up fine but seems to not have much power. Barely does 4 knots at 3000 rpm on very calm waters with no wind. Is this normal ? I purchased the boat used so I have no idea how fast it was new. Any suggestions on how to improve performance or tuneups rebuild etc ?Thanks,Nick

 

[Jim Oursler]

Yanmar 1GM Power

I bought the Yanmar Manual in hopes of solving my own problem and finally turned it over to the shop.. Looking though on page 1-7 of the manual.. at 3000 RPM output is 4.3 HP while at 3400 (max rating) output is 6.5 HP.SO the question is why can't you get to 3400.. I would call the local mechanic and save about 6 hours of activity..

 

[James Marohn]

Tuning your engine

I've recently bought an engine manual published by Solec from amazon.com:http://www.amazon.com/exec/obidos/ASIN/0893300497/o/qid=972262370/sr=8-1/102-2763398-7466523In in gives you detailed step-by-step instruction (with clear diagrams and pictures) on how to tune up and maintain your Yanmar GM engine. I am currently cleaning my fuel injectors (my 3GM has 3, I believe yours has 1). Over a long period of time, carbon deposits around your fuel injectors can alter the spray pattern in the combustion chamber, leading to decrease in engine performance.My engine is an '89, not knowing whether the previous owners has cleaned these injectors or not. Still there was quite a bit of carbon (almost looks like a tiny ant hill!).Following the book, it's not that difficult! It's actually pretty fun to get to know your engine. The book also covers many trouble shooting techniques (replacing the impellor, bleeding the fuel system of air, etc).Good luck!James MarohnPerelandraVision 32 - Seattle, WA

 

[Ed Schenck]

It's not the engine.

Granted, you should be able to reach 3400 RPM with a well-tuned engine barring any prop problems. But the fact is you are getting 3000 RPM, not bad. So I think the problem must be elsewhere. My boat displaces 18000, has a 20hp Yanmar, and does 4 knots at 1800 rpm.

 

[Jim McCue]

Is your bottom clean?

If you haven't hauled out and cleaned the bottom, you could be suffering the difference right there.Jim McCue

 

[Matt]

83 H27

I have a '83 H-27 with a 1GM. I feel its under powered for the boat, but at 2500 Rpm with a 2 blade prop I can do 4 knots. At full Rpm it will do 6.5 knots. This season we are pulling the engine to do a basic overhaul and replace the injector. I would check your fuel filters, make sure the prop isn't damaged and also check the play in the throttle cable. Good luck.