Yet one more question about 1GM and low Revs

[Dick Kobayashi]

Some years ago I had the exhaust elbow replaced and the head on the engine replaced. Engine runs just fine. But immediately afterward the engine would only rev up to 2700 rather than 3300+/- under load. So I don't think I am dealing exhaust elbow or head related problems. Each year the maximum rpm under load has dropped a little. Now it is around 2200. Please...no advice on over prop, elbows or related.

Facts:

Engine is professionally maintained

Fuel is old as I don't use more than a few gallons a season.

Runs up to 3300 w/o load so it is not the governor.

Same limitation in reverse.

Ran up to 3300 with load but a great deal of smoke before repair

Boat appears to reach close to hull speed in calm water at 2200 rpm (so have deferred attending to this)

Things I am thinking about doing

- check the accuracy of the tach on board, although I don't really think this is the problem.

- check fuel flow system (but I don't know how to).

-check to see that throttle advances fully when in gear.


Any suggestions on this most welcome.

[mgphl52]

You might want to check compression pressure. Could be "leaky" rings?

[Ken Textor]

This problem has cropped up on some of my boats in the past and it sounds like a fuel issue. Specifically, you're fuel is likely full of gack, sludge and other undesirables. Much of it is likely in the fuel tank itself because the fuel filters take care of what passes through the lines. (You do have two filters, yes?) But often (not always) there is a screen in the fuel tank itself which can get mucked up and impair the pickup of the fuel. You probably won't like the solution: Pull the tank and have it cleaned by a radiator repair shop. This is an off-season project. You'll probably get through this season as is. But the problem will worsen as time goes on because the sludge does not magically disappear. It also starts plugging up the filters on a fairly regular basis. If you do pull the tank, replace the fuel line hoses too. Cheap, easy insurance. But for now, go sailing and live with the low revs. Our northern sailing season is too short to mess around with a problem like this.

kt

[Joe Myerson]

Dick,
I have many of the same problems, with the same engine. I think it's time to try Ken's remedy.

==Joe

[Keith]

Hi Dick,

I had a similar problem when I replaced the head gasket and had work done on the head. It turned out that the injectors were not fully seated in the new copper seats. Once I got then seated the RPMs came back.

Keith

[Joe Myerson]

Hi Dick,

I had a similar problem when I replaced the head gasket and had work done on the head. It turned out that the injectors were not fully seated in the new copper seats. Once I got then seated the RPMs came back.

Keith

FWIW, I had the head gasket replaced several years ago. It didn't seem to affect the RPMs at the time. My revs started dropping later.

[mgphl52]

I'm also going to lean towards fuel supply issues. The only way I've heard of to test/prove that is with a vacuum gauge on the fuel line.