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Thread: Yanmar Diesel generator won't start.

  1. #1
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    Yanmar Diesel generator won't start.

    I've been given a Mosa 6KVA diesel generator that has been sitting unused for at least 5 years.

    IT has a Yanmar L100 AE single cylinder mechanical injection Diesel.

    I have no idea where to start on diesels, I put a new battery in it, changed the oil, rinsed out the fuel tank and put some fresh diesel in an turned the key, it started almost immediately but then choked out and died, when turning over there is no smoke indicating it's getting fuel.

    The electric fuel lift pump is working, it's getting fuel to the mechanical fuel injector pump, but it doesn't seem to be getting fuel to the injector, when I loosen the fuel line going from the mechanical pump to the injector and turn it over there's no fuel coming through the high pressure line, if I loosen the fuel line from the pump there is also no fuel coming out of the mechanical pump that I can see either.

    Is this most likely a priming issue? or something gone astray in the pump, or just some gunk built up in either the pump or the fuel line between the pump and injector?

  2. #2
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    Re: Yanmar Diesel generator won't start.

    There is only 2 things a healthy diesel needs, air and fuel. It started then stopped so you have air. If it were mine, I would change the fuel filter and use a new gasket. Then follow the bleed procedure in the manual. No manual? Crack the fuel line at the injector. Make sure you have eye protection and gloves then crank the engine until fuel squirts out of the line then tighten the fitting. It should now start. If it is a glow-plug engine, check the fuse. You might have to remove the plug from the block and see if it heats up. The fuel itself may be crappy after sitting.
    If none of that works, check the valve clearance, remove the injector and have it serviced. Good luck!
    Do not believe everything that you think.

  3. #3
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    Re: Yanmar Diesel generator won't start.

    Have you watched the YouTube videos on the Yanmar one cylinder,, like this one? (his will not start,, either)



  4. #4
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    Re: Yanmar Diesel generator won't start.

    Quote Originally Posted by Xsbank View Post
    There is only 2 things a healthy diesel needs, air and fuel. It started then stopped so you have air. If it were mine, I would change the fuel filter and use a new gasket. Then follow the bleed procedure in the manual. No manual? Crack the fuel line at the injector. Make sure you have eye protection and gloves then crank the engine until fuel squirts out of the line then tighten the fitting. It should now start. If it is a glow-plug engine, check the fuse. You might have to remove the plug from the block and see if it heats up. The fuel itself may be crappy after sitting.
    If none of that works, check the valve clearance, remove the injector and have it serviced. Good luck!
    The fuel bleed is where I'm at, when I crack the line coming out of the injector pump and turn it over no fuel comes out so it seems the injector pump isn't working correctly, I've cracked the line between the electric lift pump and the injector pump, the electric pump works and fuel flows out when the ignition is turned on, but once I tighten that and loosen the fuel line on the outlet of the injector pump and turn the engine over no fuel comes out of the injector pump.

    So I'm trying to figure out is this just a normal priming issue, or could something be stuck inside the injector pump, so should I remove the pump and see if anything looks out of whack in there?

  5. #5
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    Re: Yanmar Diesel generator won't start.

    I have a couple of these, one runs my small bandsaw mill. They are really simple engines to work on, dont worry about getting into it.
    Make sure the throttle is in full run position, and turn over with the fuel line off. If no fuel spurting out, take the pump off and give it a good cleaning, make sure the fuel control slides back and forth.
    When reinstalling it, look in there and you'll see a little fork that engages the peg on the slide on the pump.

  6. #6
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    Re: Yanmar Diesel generator won't start.

    Try loosening the bleed screw, take the fuel tank cap off, grab a blowgun and a rag or 2 and give it a few LIGHT blasts of air to push fuel out the bleeder. Also before this check and make sure filter is full of fuel if it's a spin on type.

  7. #7
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    Re: Yanmar Diesel generator won't start.

    Quote Originally Posted by M J D View Post
    Try loosening the bleed screw, take the fuel tank cap off, grab a blowgun and a rag or 2 and give it a few LIGHT blasts of air to push fuel out the bleeder. Also before this check and make sure filter is full of fuel if it's a spin on type.
    I'm betting a stuck injection pump plunger. The cam pushed it up and it won't return. Seen that on a few Cats that sat for awhile. Disassemble and clean and it should be good to go.

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  9. #8
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    Re: Yanmar Diesel generator won't start.

    Quote Originally Posted by 12V71 View Post
    I'm betting a stuck injection pump plunger. The cam pushed it up and it won't return. Seen that on a few Cats that sat for awhile. Disassemble and clean and it should be good to go.
    That could be. On TK units that use yanmar 4 cylinders, there is a check valve that takes some pressure to overcome. A worn plunger pump won't allow enough pressure for that to happen.

  10. #9
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    Re: Yanmar Diesel generator won't start.

    I agree with 12V71, probably a gummed up injector. One nice thing about these little one banger diesels is that the head gasket is a copper ring, not a usual head gasket, you can take the head off and reinstall it with the same gasket a few times, same with the aluminum case gaskets, if you dont F them up they can be reused, these are faves for the small sailboat folks for these reasons.
    Oh, another hint. these dont have a glow plug, they usually start easy, but if it's cold, warm the intake elbow with a propane torch from the outside for a while, does the same thing.
    Last edited by Poleframer; 12-04-2021 at 10:46 PM.

  11. #10
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    Re: Yanmar Diesel generator won't start.

    Guess while I'm at it, since I've had these engines for 20 some years, I'll add to it.
    If you are working on the fuel system, once you get a good spurt coming out of the pump with the metal line disconnected, and it isnt running well, take the injector out, turn it upside down and reconnect it to the metal line and turn the engine over. You should see 4 fine mists out of the injector, if not clean the injector better.
    Timing is determined by the brass shims between the pump and the case, make sure those are clean when you reinstall it, but you can change the timing by removing or adding the shims if needed, but you probably wont need to.

  12. #11
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    Re: Yanmar Diesel generator won't start.

    Awesome, thanks everyone for the advice, I'll tackle pulling the injector pump out and giving it a clean on my next day off, cheers all for the great advice

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