2 GM F RPM

[Mark]

I have a 1984 31 Hunter with a 2gmF Yanmar, The motor will get up to about 2900 rpms out of gear and only 2200-2300 in gear if pushed higher I get dark smoke and the motor will overheat. Any thoughts as to where this problem is? New to deisels, The motor runs real well by the way. Should the motor go to 3600 in drive?

 

[Steve Dion]

You've got a case of......

Mark:You got a typical case of plugged exhaust elbow. These engines are very prone to this problem. The engine should be able to rev-up to 3600 RPM's in gear and in neutral. There is a govenor on the engine that prevents the engine from over-reving.You should order a new elbow and gasket before you start this procedure. If it turns out that your old one can be re-furbed you will have a spare. Being that your boat is in salt water there is probably also severe corrosion in the elbow too.I did this to my '85 H'31and it is not too difficult. You can look in the Photo Forum and you will see a pictorial on the process. The most difficult part is removing the collar between the exhaust manifold and the elbow itself. The threads are different (but I cannot remember which way they are). You will probably also need a vice and maybe a torch to get the two pieces apart.While you are at it you should also install a new impeller in the raw water pump and also check out your heat exchanger. Don't let this engine overheat and it will last longer than the fiberglass.

 

[Collin]

Smoking Diesel

I owned a 1985 31 for 9 year. Mine could'nt do over 2100 rpm. The reason was that the previous owner had replace the original prop with a 3 blade. However, this did not cause black smoking unless the prop had barnacles. Your problems is likely one of the following:You prop is fowled with barnacles, or a line. One or both injectors has a bad pray pattern(see your manual). The previous owner re-proped the boat and the prop shop did a bad job sizing the prop.With a relatively clean bottom, your boat should make at least 6.5 kts in calm water under full power. If she can make that speed, then it means your prop is probably mis-sized, That's really not a problem however, just don't push the throttle to the point where she smokes. Let me know if you have more questions, you can find an e-mail link at the following.www.cccdelivery.com

 

[Gordon Torresen]

2GMF RPM

The 2GM should turn 3600 in neutral. If you can turn 3600 in gear, your prop is too small. Ideally you should lug down at 90% to 95% of the governor setting. Steve Dion has given you the most common reason for sluggishness accompanied by black smoke. There could be many more reasons, but try cleaning the exhaust elbow first.

 

[Richard]

smoke

Most of the time it is a fouled prop. But it could be a clogged exhaust elbow. The exhaust elbow will need to be cleaned or replaced about every 250 operating hours. Cold water in the exhaust elbow causes carbon build up in the gas port side....of the elbow.....