Yanmar Diesel Decelerates

[Dave Lewis]

I have a one cylinder yanmar 1GM diesel engine on an '83 Hunter 27. Since I've owned the boat I've had a problem where it decelerates dramatically (occasionally to the point of stalling) on its own. When I start it up, it will often rev up to 3,500 but then, without my touching the throttle, drop down as low as 1,200. I've read some postings here on this problem by other yanmar owners, and as a result have replced the mixing elbow, which can get clogged and cause this problem, and I have siphoned out the old fuel and replaced it (tyhory being thet bad fuel was causing the problem). Engine was serviced in the last 2 months with all new filters, etc. None of these things has solved my problem.Any suggestions as to what might be causing this? Also, the 1GM is definitely underpowered when it is working to capacity - any simple ideas on how to soup it up a bit?

 

[Joe on Alure]

First, isolate the problem

First, determine whether the trouble is in the cable or the engine: a loose, weak throttle cable will loose its holding power........ check that first by putting some pressure via a pair of vicegrip pliers on the cable, anywhere, and see if she still does it. take a chance with the easiest fix first. if that solves the problem, put a lug onto the cable. let us know of your progress. Joe

 

[Mark M Smith]

You have an air leak

in the fuel lines.The cable could be the problem also, but think of thisit makes more sence that the loss of rpm has to do with an air leak,...Head Gasket, High pressure pump,..Injectors,...than a Stuck throttle.

 

[Gil C. - the Wanderin' One]

Some possibilities.....

On my old '77 H27 I had simular engine problems, and more. My cable was attached to a 2X4 with a 'U' clamp that frequently came loose, so look at that. Also, the engine head developed a worm hole. I doped it up with gasket seal and it ran OK for a few more years.The new owner replaced the head a couple years after he bought the boat from me. Mack Boring in Middleboro MA has any parts you may need. Their # is 800-622-5364. You may want to get a service manual from them also for torque values, parts diagrams, etc. They said (several years ago) that the head is usually good for about 15-20 years. Sorry I don't know any to 'soup it up'. Good luck.