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Thread: Briggs Stratton Engine start's but won't run

  1. #1

    Briggs Stratton Engine start's but won't run

    Hi There,

    Have just completly rebuilt a 12F802-1975-B1 briggs engine. All new gaskets, new air filters, completely cleaned carby (including venturi holes in the nut on the bowl), reseated valves, clean oil, new fuel - basically brand new inside and out.

    Once primed, the engine will start, but then stop after 1-3 seconds. Continued priming will keep the engine going, but it stop immeditely once priming has stopped.

    I can also get the engine to run if I manually choke it , but limiting air intake.

    All this leads me to believe one of two things is happening.

    1. Its getting too much air
    2. Its getting not enough fuel

    I have checked all gaskets and seals between the air filter and intake, and everything looks fine with no obvious air leaks.

    The carby float seems to be working as intended, and the bowl is full of fuel, and all passages have been very well cleaned with carby cleaner, wire, and compressed air. So I am running out of ideas as to where the extra air might be coming from, or where the fuel is not coming from?

    Any assistance would be greatly appreciated.


  2. #2

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    Re: Briggs Stratton Engine start's but won't run

    Sounds like something is still plugged in the carb, most likely high speed circuit, may want to recheck the bowl nut jet and the emulsion tube leading up into the carb body.
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  3. #3
    I had a similar problem and my gas tank was dirty and and was not flowing through the carb properly. I cleaned the tank then carb again and put new gas in it. Purrs like a kitten now!

  4. #4

    Re: Briggs Stratton Engine start's but won't run

    Thanks for the suggestions guys. I rechecked all the holes and tubes in the carby, all like new and clean as a whistle. The tank was also completely cleaned, and new fuel line put on as well. The fuel flows freely from the fuel line when disconnected from the carby.

    Still no luck though.

    I think its about to get thrown in a river!!!! hahah.

    Any other suggestions would be appreciated. It is definately not a carb cleanliness issue though. Could it be something like a valve not sitting correctly, or timing being slightly off? The fact I can get it to run if I choke the engine (a lot), makes me think the timing and compression is probably fine. But I really have no other ideas left.


  5. #5

    Smile Re: Briggs Stratton Engine start's but won't run

    Ended up getting it going. It was the valves in the end. When I had lapped them, I had not ground the end of the valve stems, and there was some maverick (un-metered) air getting into the head when the piston was trying to compress, hence lack of compression and too much air.

    Ground the stems and made sure there was a small (0.1-0.3mm gap) between the valve stem and push rod and it started first pull.


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