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post #11 of 21 Old 05-17-2012
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Re: Low rpm 1gm10

1gm10 max hp under load is 9 HP, 8 HP continuous at 3400 rpm. in other words, the engine tag probably reads "9/8 hp", not 9.8 hp.

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post #12 of 21 Old 05-17-2012
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Re: Low rpm 1gm10

I believe the 1GM is the perfect engine for that boat. I think that it what many have now installed. I have the 3GMD which is similar except it has 3 cylinders instead of your single.

The fuel set up should be your fuel tank, a fuel suction tube in the tank (make sure the screen is clean on the suction tube), then you should have a Racor type filter (with a water separator). From there the fuel hose runs to your engine where there will be a small filter housing with cartrige filter inside mounted on the engine (there is a bleed screw on the top of this filter, the screw uses a plastic washer to make a seal, I would replace this as they can crack- Yanmar dealer part). From the engine mounted filter a short hose (3 inches) will run to you "lift pump". The lift pump is a mechanical pump with a rubber diaphram. From the lift pump the fuel runs through a metal pipe to the fuel injector pump (this pump delivers the fuel to the injectors at very high pressure), from there there will be one metal fuel pipe to your injectors.

Go here for a manual:
http://www.yanmarmarine.com/index.cf...lboat-engines/

A couple other items:
The timing for this engine is change by putting metal shims under the fuel injection pump. I am not sure if this would limit power output if timing were not right but it might. If engine was rebuilt or a new/rebuilt fuel injectioin pump were installed- the timing should be checked. Maybe go back to shop that rebuilt engine and speak with them.

The other day I was talking to some commercial fishermen. They told me they have had problems with debris clogging the 90 degree fittings they have in there fuel lines which leads to low power. I doubt this is your problem but worth going through you fuel system to make sure all is clear.
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Last edited by casey1999; 05-17-2012 at 01:47 PM.
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post #13 of 21 Old 05-17-2012
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Re: Low rpm 1gm10

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Originally Posted by casey1999 View Post
.....The other day I was talking to some commercial fishermen. They told me they have had problems with debris clogging the 90 degree fittings they have in there fuel lines which leads to low power. I doubt this is your problem but worth going through you fuel system to make sure all is clear.
Worth checking for sure.. not only for pluggage/blockage, but for leakage between the fuel level and the fuel line leaving the tank. We've experienced issues with a kinked pickup tube; a friend had endless issues with air in the fuel unless he had a full tank. We finally found the pickup tube had pinholes in it (no idea how that happened....) that were no issue if the fuel level was above them, but the moment the fuel tank dropped the system was pulling air in. Nasty to find, that one...

Ron

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post #14 of 21 Old 05-17-2012
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Re: Low rpm 1gm10

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Originally Posted by casey1999 View Post
I believe the 1GM is the perfect engine for that boat. I think that it what many have now installed. I have the 3GMD which is similar except it has 3 cylinders instead of your single.

The fuel set up should be your fuel tank, a fuel suction tube in the tank (make sure the screen is clean on the suction tube), then you should have a Racor type filter (with a water separator). From there the fuel hose runs to your engine where there will be a small filter housing with cartrige filter inside mounted on the engine (there is a bleed screw on the top of this filter, the screw uses a plastic washer to make a seal, I would replace this as they can crack- Yanmar dealer part). From the engine mounted filter a short hose (3 inches) will run to you "lift pump". The lift pump is a mechanical pump with a rubber diaphram. From the lift pump the fuel runs through a metal pipe to the fuel injector pump (this pump delivers the fuel to the injectors at very high pressure), from there there will be one metal fuel pipe to your injectors.

Go here for a manual:
Sailboat diesel engines are the lightest and toughest solutions available - Yanmar Marine

A couple other items:
The timing for this engine is change by putting metal shims under the fuel injection pump. I am not sure if this would limit power output if timing were not right but it might. If engine was rebuilt or a new/rebuilt fuel injectioin pump were installed- the timing should be checked. Maybe go back to shop that rebuilt engine and speak with them.

The other day I was talking to some commercial fishermen. They told me they have had problems with debris clogging the 90 degree fittings they have in there fuel lines which leads to low power. I doubt this is your problem but worth going through you fuel system to make sure all is clear.
Use this manual, I think this is your engine:
http://j30.us/files/yanmar-manual.pdf

Note under trouble shooting it does say inproper timing could lead to low power output. I would also have the governor control looked at. It might be worth a few hours of a yanmar mechanic to have a look at your engine, could be a simple fix. Let us know what you find.
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post #15 of 21 Old 05-18-2012
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Re: Low rpm 1gm10

I have a Yanmar repair manual for the GM series which covers the 1GM. Looking through the manual on the fuel system it states not being able to get to full output on the engine could be due to a worn fuel pump plunger. This plunger is located in the fuel injection pump (not the mechanical lift pump also mounted on the engine) The manual says to replace the plunger and the barrel as a set. This is intricate work to work on the fuel injection pump. Maybe you could take it out and send it to a shop for rebuild. This fuel injection pump is also connected into the governor. There are a lot of springs and linkages between the two (springs and linkage inside engine).

If you find no problems with fuel system (tank, filters, hoses, connections, fule lift pump) or gear/throttle linkage, then I would look at the fuel injection pump and governor.

It would being interesting to know the history of your engine. Why was it rebuilt, did it have a problem. Can the rebuilder help you out?
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post #16 of 21 Old 05-19-2012
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Re: Low rpm 1gm10

Do you have primary and secondary filters? are the bottom and prop clean? Is the stop cable all the way in?

I had a very similar issue in my 2GM20F and it was air in the fuel, not enough to kill the engine but enough to reduce performance (low max RPM). The culprit in my case was air in the primary filter (the one closer to the tank), it was half empty when I open it.

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post #17 of 21 Old 05-20-2012
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Re: Low rpm 1gm10

All great suggestions! However, have you fully applied the KISS principle?

I just went through something fairly similar with my 1GM10. Over the winter i replaced my copper fuel lines with hose purchased online. Unfortunately, this hose was slightly to big enough and i ended up having to get hose at the local marine store. All they had was silghtly too small enough, but I got it to fit enough to get a clamp on it.

Bled everything from tank to injector, hit the button and it started right up BUT wouldn't rev under load any higher than about 2100 rpm. I went through everything again to check for air leaks, still no revs. I replaced the fuel filters twice, even though the first pair were put in fresh for Spring Commission. I even went so far as to pull the injector and ended up replacing it as the shaft wouldn't slide in the cylinder. No joy on the revs.

Engine and drive train ran fine last year, all i did to muck it up was to replace the fuel lines. Couldn't (shouldn't) be prop, trans, fuel injector, lift pump, filters, rings, pistons, etc. Had to be something I touched. 3 days later, after going over the whole engine multiple times, i bled the flappin thing again, One. Step. At. A. Time.

Runs like a top now. Make no mistake, ANY air in the system will haunt you! I'd suggest bleeding it again thoroghly!
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post #18 of 21 Old 05-21-2012
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Re: Low rpm 1gm10

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Originally Posted by cspaniel View Post
Do you have primary and secondary filters? are the bottom and prop clean? Is the stop cable all the way in?

I had a very similar issue in my 2GM20F and it was air in the fuel, not enough to kill the engine but enough to reduce performance (low max RPM). The culprit in my case was air in the primary filter (the one closer to the tank), it was half empty when I open it.

Goo luck
Could be the problem. This filter housing is aluminum, can corrode and be hard to seal (even with the o-ring). There is an o-ring seal for the filter bowl and a washer seal (two) for the bleed screws at the top (maybe these are missing or cracked- they are plastic). I bought an entire new unit for mine (Yanmar part # for the 1gm is 124790-55601, about $50).

For bleeding I have a Moeller squeeze bulb at the tank, use that to pump fuel through the racor and all the way to engine. At engine I have a bypass line (can isolate with shut off valve) that send the fuel back to tank via engine fuel return line). This way I can prime system right up to the engine mounted fuel lift pump. Once primed to the lift pump, I use that to bleed system to the engine mounted fuel filter (use bleed screws at the top of the filter), use bleed to the engine filter, crack the fuel line on the fuel injection pump and bleed to that (use lift pump by hand to pump fuel), then crack the fuel line at injector, run engine with raw water off and engine shut off engaged (so engine does not start), run until fuel comes out of injector line then tighten.

Last edited by casey1999; 05-21-2012 at 12:55 PM.
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post #19 of 21 Old 05-25-2012 Thread Starter
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Re: Low rpm 1gm10

Thanks all! Lots of things I didn't think of and learned a lot. I think I got it fixed but I still might get a tachometer so I can test more fully. But the good news is I got power!

The shaft turned very easy by hand when in neutral so that eliminated the friction possibility.

I ordered a lift pump thinking it was weak but haven't installed it yet because I think I solved it with an alternate bleeding technique I think suggested by jkkimberly. At the fuel injector I would open more than a partial turn when bleeding so I think that maybe air would immediately leak back in once I stopped cranking. Once I just "cracked it" life got better the engine started easier and a bit more power.

That wasn't all though. As I was bleeding I noticed that the fuel strainer had small amounts of fuel leaking at the seam and drips were actually forming on the bottom. At closer inspection this was leaking at the cup and the bleed screw was stripped out a little. So I replaced the full fuel strainer assembly and then the lift pump felt more powerful when bleeding and fuel was squirting all over rather than just dribbling out at the fuel strainer and the injection pump. So a faulty fuel strainer seal was to blame too.

I also replaced the fuel line from the tank to the engine. This was just an old line so thought it was a smart thing to do.

Then I noticed that it was capable of higher rpm in reverse than in forward and did some re adjustments on the remote control which equalized them more. I took it out for a spin and at first it was slow but by the time I got about 30 min of run time there was even more power so I think the folding prop needed some cleaning. This weekend I'll dive under and check it out.

I still think that there could be some optimization as the rpms are still lower than the no load case by a fair bit. I think I'll have a mechanic check out the timing and governor set up but in the time being I should be off and running with confidence.

Many thanks!!
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post #20 of 21 Old 05-29-2012
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Re: Low rpm 1gm10

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