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Old 23-03-2012, 05:55   #1
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Yanmar 2GM will not go above 800 RPM in gear

Starts up easily
Runs smooth
Can get 2800 RPM in Neutral
Can’t get over 800 RPM in Gear
Not over pitch because we got 3000 RPM with this propeller before problem started

Propeller is clean
Bottom of boat is clean.
Mixing elbow is clear
Fuel tank, filters and lines were just cleaned out
The throttle/ fuel supply control is fully forward at the motor

Very desperate for ideas….
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Old 23-03-2012, 05:59   #2
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Re: Yanmar 2GM will not go above 800 RPM in gear

drag from stuffing box or cutlass bearing?
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Old 23-03-2012, 06:16   #3
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Re: Yanmar 2GM will not go above 800 RPM in gear

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drag from stuffing box or cutlass bearing?
Thanks. Not sure how to check this. The propeller shaft spins very freely.
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Old 23-03-2012, 06:25   #4
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Re: Yanmar 2GM will not go above 800 RPM in gear

How hot does the trans get while running in gear? (120º F Max.)
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Old 23-03-2012, 06:29   #5
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Re: Yanmar 2GM will not go above 800 RPM in gear

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How hot does the trans get while running in gear? (120º F Max.)
Thanks for the input...

Not sure, Will have to check.
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Old 23-03-2012, 06:50   #6
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Re: Yanmar 2GM will not go above 800 RPM in gear

There are a few more questions to be asked:
1. Is the air intake clear?
2. Has it started smoking more then usual?
3. When did it start? After replacing the fuel filters? After a long period of inactiveness? All the sudden?
4. How old is the Fuel?
To me there are only 2 things to consider, Fuel problems, (bad fuel, bad injector(s) bad injector pump, possible blocked filter, sometimes the fuel flow is poor even in a new one, or air in the fuel system) or one of your cylinders has lost compression.
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Old 23-03-2012, 06:54   #7
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Re: Yanmar 2GM will not go above 800 RPM in gear

Another potenal problem may be a bad lift pump or fuel pump.
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Old 23-03-2012, 07:13   #8
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Re: Yanmar 2GM will not go above 800 RPM in gear

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Another potenal problem may be a bad lift pump or fuel pump.
Air Cleaner is new

Not smoking



when did it start? ___ Long story, I will try tu summerize...

Motor was running A OK, Then would not start. Marina found water in the fuel. They removed, cleaned and re-installed the tank, replaced fuel lines and filter and new fuel.

Now motor starts but...... Will not go past 800 RPM in gear.
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Old 23-03-2012, 07:55   #9
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Re: Yanmar 2GM will not go above 800 RPM in gear

My thinking goes like that: very little fuel is needed to start the engine. Also only slightly more is needed to rev the engine without load applied. But it takes much more fuel to perform any actual work. Since engine starts easily and idles smoothly I would look at fuel delivery problems. To dive further you will need to isolate the problem area. I would start with disconnecting fuel supply at the injection pump and gravity feed the pump directly from a small (and very clean!) tank. If with this setup engine revs under load, problem is before the pump. If not, pump and anything after it is suspect.

I assume you checked the mechanical linkage between throttle and pump.
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Old 23-03-2012, 08:10   #10
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Re: Yanmar 2GM will not go above 800 RPM in gear

MRM is correct, I would look at the fuel delivery system closely, since everything was working before the fuel problems were decovered, it would be very likely that something to do with the fuel tank removal and reinstalation may be your problem, also the fuel venting system. If no air can get into the tank when fuel is removed by the engine it can cause a suction that will cause the problems you are describing. You might try removing the fuel filler cap when testing again. It could be something as simple as a kinked fuel or vent line.
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Old 23-03-2012, 08:19   #11
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Re: Yanmar 2GM will not go above 800 RPM in gear

I have also hear of another posible cause. A fellow boater had fuel that had a lot of water in it, he tried and tried to start the engine which introduced fuel and water into the engine through the injectors, then he let it sit for a long time which caused all kinds of probems with his injectors and injector pump, rust in the cylinders and so on, but since your engine is running but will not produce power, I would not think that this is to likely.
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Old 23-03-2012, 08:21   #12
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Re: Yanmar 2GM will not go above 800 RPM in gear

Surely you should well over 2,800 RPM in neutral so I am with the fuel supply problem camp.
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Old 23-03-2012, 08:24   #13
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Re: Yanmar 2GM will not go above 800 RPM in gear

Fuel supply. Since the fuel system was recently worked on, I'd double check that the In/Out fuel lines on the filter weren't reversed. Don't ask me how I know this....
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Old 23-03-2012, 08:42   #14
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Re: Yanmar 2GM will not go above 800 RPM in gear

Fuel supply is the most likely problem. Any chance the fuel valve was not fully opened? One problem I have seen a few times that caused this type of results was a fuel hose which was delaminated on the inside causing a restriction in the line.
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Old 23-03-2012, 10:50   #15
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Re: Yanmar 2GM will not go above 800 RPM in gear

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Fuel supply is the most likely problem. Any chance the fuel valve was not fully opened? One problem I have seen a few times that caused this type of results was a fuel hose which was delaminated on the inside causing a restriction in the line.
I want to thank all of you for your helpfull input. Your thoughts support my idea that maybe my motor is not toast....

I am hopfullit's just fuel pump/pumps ir injectors.....
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