Pearson 303 – Yanmar 2GM20F only reaches 2000 with 14x10 3-blade prop

[dlarusso]

Looking for some advice on an issue w/ my '85 Pearson 303. This has been gradual but seems to have picked up over the last 3 months. Running a Yanmar 2GM20F (16hp, 3400)
/ Kanzaki KM2P 2.62:1 with 14x10 3 blade (RH). She never cruised too well over 2500 but now won't push over 2000 and the engine just sounds flat w/ a lot of grey exhaust and discharge if I push it full throttle. Raw water discharge is consistent (trap clean, flow looks good) and in neutral I can reach full RPM...so I have to imagine something is constricting the engine when engaged...but can't seem to figure it out. Mechanic said it is an over sized prop issue, but from what I'm reading 14x10 seems OK for this configuration. Good times. Many thanks for any thoughts here...

 

[dlochner]

Has anyone inspected the prop to make certain it is clean and not damaged?

 

[kappykaplan]

Has anyone inspected the prop to make certain it is clean and not damaged?

Welcome to the forum!

 

[dlarusso]

Had a diver down there a few weeks ago and he thought things looked clear and prop was ok. Will get another opinion on that. Thank you

 

[Ralph Johnstone]

Mechanic said it is an over sized prop issue,

Your mechanic seems to be your first problem. Don't let him near your engine.

I had this propellor designed and built for my H-310.
__________________________________________________________________

​

Same transmission.
_____________________________________________________________

Your Yanmar may have a congested throat :

A short history of your engine would go a looooooooong way in determining what the problem(s) are here.

Also, I mentioned a plugged mixing elbow as a first inspection because it's the cheapest in a long list of expensive solutions running from this one (~$15.00) up to buying a new fuel pump and servising the injectors all at the same time (upwards of $2,500.00).

I trust you will be checking the mixing elbow yourself for the cost of a new $15.00 gasket. It's an easy enough job but realize you may not be able to clean the old elbow which means buying a new one.

Check the archives for Plugged Yanmar Elbows. A real ballpark estimate on having the elbow checked by a mechanic and "replaced" just to "keep it clean" I would expect to be pushing $800.00. Look at a SS mixing elbow which few mechanics will tell you about. About 50% the cost of a Yanmar mixing elbow.

Let's see how long it takes for someone to suggest replacing the pump and injectors as your first check. There's always someone

 

[garymalmgren]

Hi dlarusso
and welcome aboard.
RE; .so I have to imagine something is constricting the engine when engaged

Your boat/engine is 40 years old. That would indicate something time and use related.

Ralph has clearly identified a blocked or corroded exhaust elbow. So my advice is to follow his advice.
I reckon that he is on the money with that one.
This a job that you can do yourself. That will save time and money and get you more familiar with your engine.

All the best
gary

 

[dlochner]

Let's see how long it takes for someone to suggest replacing the pump and injectors as your first check. There's always someone

Ralph, Why do a job half way. This calls for a complete rebuild of the engine, new injectors, pumps, rings etc etc. That's the only viable solution for the Marine Technician's Benevolent Union.

Seriously, the injector elbow is a good candidate for inspection and cleaning if necessary. If it does need replacing because the metal is getting thin or the carbon build up is too thick to clean get a SS elbow and be done with it. HDI Marine is the place to go for a new elbow.

Try changing your fuel filters. A clogged filter will restrict the fuel supply and reduce the motor's power. Besides, it is always good to change the filters once in a while.

I don't think the prop is the issue. An over pitched prop will cause the engine to load up and the exhaust will be black not gray.

 

[dlarusso]

Your mechanic seems to be your first problem. Don't let him near your engine.

View attachment 238877​

I had this propellor designed and built for my H-310.
__________________________________________________________________

View attachment 238878
​

Same transmission.
_____________________________________________________________

Your Yanmar may have a congested throat :

View attachment 238874​

A short history of your engine would go a looooooooong way in determining what the problem(s) are here.

Also, I mentioned a plugged mixing elbow as a first inspection because it's the cheapest in a long list of expensive solutions running from this one (~$15.00) up to buying a new fuel pump and servising the injectors all at the same time (upwards of $2,500.00).

I trust you will be checking the mixing elbow yourself for the cost of a new $15.00 gasket. It's an easy enough job but realize you may not be able to clean the old elbow which means buying a new one.

View attachment 238876


Check the archives for Plugged Yanmar Elbows. A real ballpark estimate on having the elbow checked by a mechanic and "replaced" just to "keep it clean" I would expect to be pushing $800.00. Look at a SS mixing elbow which few mechanics will tell you about. About 50% the cost of a Yanmar mixing elbow.

View attachment 238879​

Let's see how long it takes for someone to suggest replacing the pump and injectors as your first check. There's always someone

Ralph - this is great thank you so much. This will be next step for sure. Really appreciate the depth of this feedback and insight. May take me a few weeks to sort, but I'll come back here with updates as I can. Many thanks.

 

[dlarusso]

Ralph, Why do a job half way. This calls for a complete rebuild of the engine, new injectors, pumps, rings etc etc. That's the only viable solution for the Marine Technician's Benevolent Union.

Seriously, the injector elbow is a good candidate for inspection and cleaning if necessary. If it does need replacing because the metal is getting thin or the carbon build up is too thick to clean get a SS elbow and be done with it. HDI Marine is the place to go for a new elbow.

Try changing your fuel filters. A clogged filter will restrict the fuel supply and reduce the motor's power. Besides, it is always good to change the filters once in a while.

I don't think the prop is the issue. An over pitched prop will cause the engine to load up and the exhaust will be black not gray.

Thank you Dave, will check/replace the fuel filters as well!

 

[dlarusso]

Hi dlarusso
and welcome aboard.
RE; .so I have to imagine something is constricting the engine when engaged

Your boat/engine is 40 years old. That would indicate something time and use related.

Ralph has clearly identified a blocked or corroded exhaust elbow. So my advice is to follow his advice.
I reckon that he is on the money with that one.
This a job that you can do yourself. That will save time and money and get you more familiar with your engine.

All the best
gary

Thank you, Gary! Let's see how well I can do here...Much appreciated.

 

[Ralph Johnstone]

Ralph, Why do a job half way. This calls for a complete rebuild of the engine, new injectors, pumps, rings etc etc.

Fat lot of good that will do .

You forgot to replace the most important part, the exhaust fan and hose.

Have you forgotten the creed of the Marine Technician's Benevolent Union when it comes to engine overhauls :

"IF A LITTLE BIT'S GOOD, A WHOLE LOT'S BETTER"​

 

[mschreib1]

I have the same engine on my Hunter 31. When my prop (2 blade) gets overgrown with barnacles I get a lot of black smoke at full throttle and my max speed can drop in half. I take care of it myself by taking a swim with a putty knife to scrape it clean. Apparently when the diesel is working too hard, the fuel burning efficiency drops and black smoke results. Full throttle in neutral tells me it’s the prop and/ or the shaft causing the restriction.

 

[Benny17441]

That is a symptom of a fouled prop. Make sure it is clean and has not been damaged. A hull bottom full of sea growth can also add resistance. The smoke you may see is due to overfueling, the governor responds to the increased load by releasing more fuel but with no mechanical increase of RPM the combustion is incomplete.

 

[Ralph Johnstone]

That is a symptom of a fouled prop.

Had a diver down there a few weeks ago and he thought things looked clear and prop was ok.