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Thread: C90 Primer layout

  1. #1
    giangab's Avatar
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    C90 Primer layout

    Hello Guys,
    My PA18-95 restoration is nearing the goal.
    I have an overhauled C90-12f for which the Stromberg carb has been replaced with a newly overhauled Marvel Schebler MA 3SPA.
    The primer pump nozzle for the Stromberg was placed on the intake manifold near the carb flange.
    My mechanic claims that for the MA 3SPA is no use to put the nozzle in the intake manifold as this carb has an acceleration pump. He says we need two nozzles, one each for cylinder 1 and 3, for which there is a threaded attachment on the cylinder head (between valve cover and upper spark plug, now plugged).
    I have searched for this primer layut, but found nothing.
    Help please!
    Thanks, Gian
    Likes jrussl liked this post

  2. #2
    cubdriver2's Avatar
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    It works just fine on the intake manifold if you need it. Most of us never use it for cold starts, just pump the throttle twice does the same thing. Some don't even put it back in the plane after adding a Marvel carb. I think it should stay because if you have a fuel problem between the gascolator and the carb you still might be able to prime your way home.

    Glenn
    "Optimism is going after Moby Dick in a rowboat and taking the tartar sauce with you!"

  3. #3
    mvivion's Avatar
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    Your mechanic is right, there should be fittings on the cylinders for prime. I’d do as he says. I always prime for cold starts....simple and when hand propping it starts third blade every time. Working the throttle while cranking is generally okay, using the accelerator pump to prime, but doing so when not turning the engine over, as in hand propping, drops a lot of fuel down into the air box. I prefer to get the prime into the cylinders, where it’ll do some good.

    MTV

  4. #4
    cubdriver2's Avatar
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    Works just fine. 4000+ hand propped hours and starts 3rd blade everytime.

    Glenn
    "Optimism is going after Moby Dick in a rowboat and taking the tartar sauce with you!"

  5. #5
    BC12D-4-85's Avatar
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    Priming the induction spider on a small Continental via carb pump or primer works - but if it's cold outdoors and the engine parts not warm much of the fuel won't vaporize and will condense before it reaches the combustion chamber. Fuel dripping from the airbox is one sign.

    My experience has convinced me for winter flying priming the cylinders makes starting better. What's cold? Even at +30F direct cylinder priming works more consistently for me. Four planes worth of obs.

    Gary

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