John Deere 420 lawntractor won't idle
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Thread: John Deere 420 lawntractor won't idle

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    John Deere 420 lawntractor won't idle

    My 420 JD lawn tractor runs well wide open but I can't get it to idle. Any thoughts?

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    Depending on the rpm it might just be an idle screw adjustment.


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    Or crap in the idle jet.

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    jackson63 (06-19-2019)

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    Run some Seafoam through it. It will cause it to throw white smoke but that's ok. A lot of times that will get any junk in the carb passages out. I will spray right down the carb or you can pour some into your tank.
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    Jackson63,

    Don't forget that these little Onan twins are specified by Deere to 'idle' at 1350 RPM which may seem fast to some, but gives a smooth "no load" speed.

    Has this tractor just started to have idle issues where it was fine before, or is it 'new-to-you' and you are just getting started in using it? If it is surging or hunting at slow speed another thing to check is for air leaks in the manifold -- these manifolds are made in two cast pieces and often develop leaks after a few decades. There are many threads here and on WFM about repairing the Onan manifold. Here is a typical one...

    Onan intake manifold

    Chuck
    rydplrs and 69project like this.

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