2GM power loss

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Nereussailor

Nereussailor

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Mar 22, 2004
733
Hunter 30 Vero Beach
Hi all,
I've got a Yanmar 2GM that is in my 83 H30 that is raw water cooled. I'm not sure how many hours are on the motor, because it did not have an hour meter on it when I bought it. The motor runs great, starts great, and pushes the boat along good. The problem I'm having is it doesn't seem to have a lot of power. At full throttle, I can only get it up to 2400 rpm's. It has a new transmission, shaft, cutless bearing, and the prop is clean, so it's not any of those things. It has a new fuel pump, so it's getting plenty of fuel. The air filter is clean and in good shape, so we can count that out too. After that, I'm at a loss as to what it could be. I've read posts in th past about the same problems, but can't seem to find them now. So any thoughts?

Dave
 
Stu Jackson

Stu Jackson

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Feb 26, 2004
23,353
Catalina 34 224 Maple Bay, BC, Canada
Dave, what rpm does it do in neutral WOT?

And what do the specs for the engine say it should be?
 
zeehag

zeehag

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Mar 26, 2009
3,198
1976 formosa 41 yankee clipper santa barbara. ca.(not there)
check the elbow---it will do this when the exhaust mixing elbow is in need of cleaning or replacement.....mine did ....goood luck.......
 
BobM

BobM

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Jun 10, 2004
3,269
S2 9.2A Winthrop, MA
Zeehag gets my vote. The first time my boat won't rev up to 2800 I am pulling my exhaust mixing elbow and replacing with new.
 
Mike Holibar

Mike Holibar

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Jun 26, 2007
106
Freedom F39 Lyttelton New Zealand
Dave, in addition to Stu's question, is this a new problem or has the engine always run like this?
 
Nereussailor

Nereussailor

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Mar 22, 2004
733
Hunter 30 Vero Beach
It's a new problem,that just started in the last couple of months. I'm going to the boat today to take the mixing elbow off and see what's up. I've had the boat for 5 years, and it's never been apart. Who knows what the previous owner had done with it.

Dave
 
Nereussailor

Nereussailor

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Mar 22, 2004
733
Hunter 30 Vero Beach
Well, I've removed the mixing elbow, and haven't found anything. There was about 1/16" build up of carbon in there, so that doesn't seem to be the problem.I felt around inside the exhaust manifold, and nothing there either. I did a no load test, and the motor went up to 2700 RPM's. I looked in the service manual, and couldn't seem to find what the RPM's should be. The one table that I did find, said 3400 RPM's was the speed at which HP was tested, But that's all I could find. I'm going to check the throttle cable connection to make sure it's set right other than that, I'm still at a loss.

Dave
 
Mike Holibar

Mike Holibar

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Jun 26, 2007
106
Freedom F39 Lyttelton New Zealand
Dave, my old 2gm had a rating plate on the front of it. The ratings were 16hp continuous at 3400 rpm and 18hp maximum intermittent at 3600 rpm. If the throttle cable is giving the correct travel perhaps the problem is one of fuel starvation. Maybe take a look at the fuel filter(s)?
 
J

John Howitt

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Jul 1, 2007
169
hunter 29.5 Nanaimo BC
On my29.5 the tack seems to have only one of the two pick ups working at higher RPM's. Normal up to about 1300 top RPM is only 1800 which is half of the max. The engine runs good and has lots of power for 18 little ponies so I have no intention of changing it.
Now if I can just get the bug#&r to idle.
Do you get the boat speed that you are supposed to get?
 
S

Steve Dion

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Dec 2, 1999
15,184
Hunter Vision-36 Rio Vista, CA.
Fuel Filter? Also pull the fuel pickup tube out of the tank and check it out. There is sometimes a screen on there that could be partially blocked.

You engine SHOULD rev to 3400-3600 at WOT. If you cannot find a fuel issue, you may be better off having a Yanmar mechanic check it out.
 
Mike Holibar

Mike Holibar

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Jun 26, 2007
106
Freedom F39 Lyttelton New Zealand
John Howitt said:
On my29.5 the tack seems to have only one of the two pick ups working at higher RPM's. Normal up to about 1300 top RPM is only 1800 which is half of the max. The engine runs good and has lots of power for 18 little ponies so I have no intention of changing it.
Now if I can just get the bug#&r to idle.
Do you get the boat speed that you are supposed to get?
Click to expand
John, sorry to have to tell you this but you don't have 18 ponies with your engine setup. At 1800 rpm the 2GM20 develops 8 horsepower. It will only give you 18 at 3600 rpm. If you change your propeller to allow the engine to develop its full power you will be amazed at the improved performance and reduced fuel consumption, not to mention the end of black smoke. Always assuming your tacho is accurate. As I re-read your post the tacho could be reading half speed.
 
J

John Howitt

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Jul 1, 2007
169
hunter 29.5 Nanaimo BC
The tack is reading half speed. I have a three blade cambell sail prop and have a boat speed of around 6 knots depending on wind, tide, etc.
No complaints here. It seems I have an issue with the fuel pick-up though.
 
R

RobJ74

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Mar 9, 2008
23
Hunter 29.5 Captain's Cove, Ladner BC
John...

As you know I have your old prop on my boat and I'm getting 7.5 knots (using GPS and Knot Meter) at 2800 RPM. I'm just waffling on this Campbell Sail Prop as I think I'm going to lose boat speed under sail and power. What did you get with this old prop? I'll try and give you a call again before I put my creditcard down on this new one from West by North.
 
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