Yanmar 2GM20F High revs & Lack of power ?

[Jollybot]

Yanmar 2GM20F with high revs and low power ?
Did have smoke in the cabin but obviously turned off engine. Cleaned out jets as well as we could, but issue still persists. Any thoughts?

 

[Tranona]

More information required. What do you mean by "jets"? How do you define high revs and low power - in gear under load? What boat and what speed are you getting?

 

[Jollybot]

Hi.. I’m referring to the diesel jets.
Starts well but under load and after c. 150 mtrs, it’s gets slower but revs remain high.

 

[bignick]

do you have a shaft drive or a sail drive?
Possible gearbox problem?

 

[Boater Sam]

Hi.. I’m referring to the diesel jets.
Starts well but under load and after c. 150 mtrs, it’s gets slower but revs remain high.

No such thing as diesel jets, what are you referring to.

 

[Tranona]

Hi.. I’m referring to the diesel jets.
Starts well but under load and after c. 150 mtrs, it’s gets slower but revs remain high.

OK - those are the fuel injectors.

Are you saying the boat speed falls for any given revs? If so the problem is probably not with the engine but the transmission - gearbox, shaft, propeller. Details of the type of transmission and boat would help.

 

[neilf39]

Clutch cones slipping under load?

 

[webcraft]

Propellor slipping on shaft? (Key sheared)

 

[Tranona]

Could also be the shaft turning in the clamp coupling.

 

[scozzy]

So I have a 1gm so not exactly the same but....same enough in this instance.....recently my engine jumped into high revs,no power delivered to propshaft and had to reach in and manually pull back on kill cable to stop engine as no joy on lever sitting in usual spot..was bouncy and windy and there i was on my knees in the cabin......oh thr joy...the culprit?? The fuel return line from top of injector back to tank jubilee clip had gone sth and once replaced and tightened up ,away she went back to happy idle and performed as it should..so..maybe check fuel lines in and around injector/s?

 

[Jollybot]

Thanks all .. appreciate the input.
When I have more news I’ll update you.

 

[Jollybot]

do you have a shaft drive or a sail drive?
Possible gearbox problem?

Hi … sorry about the delayed reply.
The boat has a shaft drive.

 

[Jollybot]

OK - those are the fuel injectors.

Are you saying the boat speed falls for any given revs? If so the problem is probably not with the engine but the transmission - gearbox, shaft, propeller. Details of the type of transmission and boat would help.

Morning .. apologies for the delayed response.
She’s a Hunter 320 sailboat with shat drive. .. would you have any thoughts ?

 

[Jollybot]

OK - those are the fuel injectors.

Are you saying the boat speed falls for any given revs? If so the problem is probably not with the engine but the transmission - gearbox, shaft, propeller. Details of the type of transmission and boat would help.

Apologies for the delayed response.
She’s a hunter 320 sailboat with shaft drive and cone style clutch.
The more the engine has to work, the more I have to increase throttle level. The revs re mail high, but I’m not travelling as fast.

 

[bignick]

The most likely culprit is a slipping clutch. At moderate load it just about holds, with minimal slippage. As you increase throttle you increase torque and the clutch starts to slip.
Ideally you want to measure the output shaft speed using a tachometer. There was a similar thread a while back, where someone found one you can run on an iphone. I’ll see if I can find it for you.
The other thing you will need to know is your gearbox ratio, so you can calculate if it is slipping.
Other sources of slipping, such as the coupling, can show similar behaviour. They’re much easier to eliminate, so may be worth doing first. Mark both sides of the coupling with paint or a marker pen, They shouldn’t move relative to one another. Go for a fast run and then check again.

 

[bignick]

Have a look at this thread:
Lost of speed

See post #21
@Pye_End recommends an app called ‘RPM meter strobe light’