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  1. #1
    Join Date
    May 2004
    Location
    Sunshine Coast Queensland
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    53
    Posts
    1,400

    Default Mower Won't Idle

    I got given a lawn mower, an older Rover with a Briggs and Stratton engine.
    From the appearance I could see it hadn't been looked after so before starting it I pressure cleaned it, changed the fuel/oil and cleaned the plug and air filter.
    It starts and runs fine, but won't run below about half throttle - the throttle has full movement but pull it back below half and it's like the engine has been switched off.
    It is old but its decent quality so if I can fix it myself (I have basic mechanical knowledge) I'd like to.
    Would it need a full carb kit or could it just be junked up.
    Cheers

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  3. #2
    Join Date
    Jun 2010
    Location
    Bundaberg
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    Default

    Might just need tuning, but throwing some carby cleanerthrough it won't hurt. Looks like your pilot jet is the one that is misbehaving.

    There are two jets in the carby; the main jet which takes care of the upper 2/3 of the throttle and is usually a drilled orifice that rarely ever needs to be changed. As the mower runs at high throttle openings that won't be the problem. Usually this can't be adjusted without dismantling the carby but small cheap ones like on a chainsaw or whipper snipper will have an adjustable air screw.

    The pilot, or idle jet; is used for the first 1/3 throttle. This one is totally fixed and can't be changed but the air flow across it can be adjusted; there will be a screw sticking out the side somewhere of the cary; it may look like a post with a knurled head and a screwdrive slot cut in the end. This is what you need to adjust to get your mower running better. The screw will have a basic pre set position; something like "fully screw it home then back it out two turns".

    Finally; there will be a screw to adjust the throttle position at idle.

    Basically; you pre-set the pilot jet; then get the mower running. Once warmed up you find the ideal pilot jet position by winding it in until the mower starts to complain; then wind the screw out again and past the pre-set until again the mower complains. The desired setting will be between the two. Open the throttle full; if it stumbles a bit but then picks up you need to tweak the pilot jet out an 1/8th turn at a time until it gets better. If it gets worse... go the other way

    Once the pilot is set adjust the idle speed.
    Nothing succeeds like a budgie without a beak.

  4. #3
    Join Date
    May 2004
    Location
    Sunshine Coast Queensland
    Age
    53
    Posts
    1,400

    Default

    Thanks for the advice, the solution turned out to be stupidly simple.
    The carb is mounted on top of the fuel tank, I noticed the fuel tank wasn't sitting right due to a missing bolt. It was obviously pulling on the throttle cable because when I fixed the missing bolt it runs fine.
    I got this mower for free, it's an older rover with a briggs & stratton engine so it should run forever, but the previous owner didn't look after it - I pressure cleaned enough garbage off the underneath to half fill a 20L drum, and the attached pic is the blades that came off it.blades.jpg

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