Js550 Front Cylinder Lean but Leak Down Test is Good

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  1. #1
    PWCToday Newbie JetSkiJunkee's Avatar
    Join Date
    Jul 2018

    Js550 Front Cylinder Lean but Leak Down Test is Good

    I have a 1985 js550 that I have rebuilt. New crank and top end along with all new seals and gaskets. The front cylinder is running lean and will cause a runaway condition on the stand but not in the water. I have blocked it off between the carburetor and intake manifold and also between the cylinder housing and the exhaust manifold. It holds 9 psi all day. This is the second time I've pulled the motor to check it. I also sprayed stating fluid around the carb last time I had it running as suggested on here to see if it was leaking from the carb and I got no response. I guess Im wondering if I can do a leak down test by blocking off the top of the carburetor or will this mess up something in the carb? Should I put air through the fuel intake? Any ideas would be appreciated.

  2. #2
    PWCToday.com Is My Home Away From Home john zigler's Avatar
    Join Date
    Mar 2003

    Re: Js550 Front Cylinder Lean but Leak Down Test is Good

    I would not pressurize the engine with the carb on.

    Just a thought...

    I currently have Reed 550 here in the shop I am building. This cyl has a piece of casting blob the size of a RASIN in one of the transfer ports. I have never seen anything like this, and cannot believe it ran like this, as it did since 1994. I would sure think something like this would give a lean condition on one cyl.

    If your engine holds 9psi, you are tight, and good to go there.

    Runaway condition is NOT good. You may have carb, or fuel feed issues as well. Check your pick ups in the tank, tank valve, fuel select, carb internals, etc.
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  3. #3
    I dream skis
    Join Date
    Jan 2007
    Earth (but just visiting)
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    Re: Js550 Front Cylinder Lean but Leak Down Test is Good

    Mabe you should try pulling a vacuum on it instead of pressure.

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