My Yanmar 2GM won't rev past 1,000 RPMs

[Nelsonhow]

The 2 GM on my 1983 H-30 won't revpast 1,000 RPMs. I used to max out at about 2,200 RPMs. I ued to max out at about 5.5 knots and now the max is about 3.5 knots so even if the cockpit RPM gague is off I think I have a problem.

The max RPM is the same in gear and in neutral.

I noticed a little whitish smoke, only at the max RPM, but is very hard to tell because the exhaust outlet is below the waterline under the boat.

The motor starts right up and runs smoothly and has never overheated or given me any problem.

The boat will be hauled for the winter next week but I can start it an run it with a bucket and hose set up for the next month or so until I have to winterize for the cold weather.....

 

[Ralph Johnstone]

Loads of Advice Available .............................

..................... on 2GM's under the search menu above.

I'm going to go way out on a limb here and say that it may be a plugged mixing elbow. Always a good place to start.

In addition, you should also max out around 3600 RPM in a perfect world.

 

[navigator97]

While 3600 is a max RPM for that engine, you should be able to run continuously at 3000 RPM with out problems or smoke. If mixing elbow has not been changed for a long while it will coke up and create back pressure and reduced achievable RPM's. It should be changed (or at least cleaned) every 500 to 700 engine hours. It's also possible that it is clogged injectors.

 

[Nelsonhow]

I meant to add this to the post. I had the mixing elbow off less than 25 running hours ago. It was clean as a whistle. I also checked the thru hull for the exhaust and it was also clear. Nothing obstructing the exhaust exit in the hull.

 

[Bill Roosa]

If it runs at 1000 then the mixing elbow will not stop the engine at idle. Can't be the mixing elbow.

 

[whatfiero]

dirty bottom , dirty prop I didn't read anyware what rpm it will rev to in neutral miss aligned strut / motor mounts ; too tight dripless (all in gear problems) dirty filters, air in system or bad fuel (simple in neutral problems)

 

[John Howitt]

I would check the throttle control. If that checks out okay, it may be the lift pump, have it pressure tested
Good luck.

 

[Nelsonhow]

1,000 RPMs in gear and in neutral. I looked at the linkage and with it running at max throttle setting is appears that the lever on the engine is in he max position.

 

[druid]

If it's only doing 1000 rpm in neutral, it's not prop or dirty bottom, and not something like mixing elbow or injectors. Hell, a 2GM is supposed IDLE at 1200 iirc.

I'd say the problem is in the high-pressure pump. Wild guess is that the throttle connection is broken (inside?) so it never gets over idle. Does the RPM change AT ALL between idle and full-throttle? (As an aside: technically it's not a "throttle" because unlike a gas engine, it does not control a butterfly valve that "throttles" the amount of air-fuel mix.It's a... ummm... fuel metering control. Or maybe speed control...)

The governor, which I believe is in the high-pressure-pump assembly, could be the culprit as well.

Unfortunately that's not an easy fix, or something a layman should attempt.

druid

 

[Sailm8]

I had this problem on a 1gm and it turned out to be a clogged fuel pick up tube.

 

[John Howitt]

The governor is on the front of the crankshaft and really can't break.
Idle should be about 850.
Re-build on the hi-pressure pump will run about $650.
Been there done that. Could not afford the shirt.

 

[Steve Dion]

Also check out the fuel pick-up in the tank. I don't think that is the problem, but it is an easy place to start. Check out all of the filters and be sure that you don't have any air leaks.

You may also want to get one of those strobes to measure the RPM's.

 

[joker460]

Just a pie in the sky suggestion. Are both compression levers fully closed?