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  1. #1

    Join Date
    Apr 2019
    Posts
    11
    Location
    Hayes, VA
    Mower
    Lawn Boy 8403 and John Deere 14SB

    8403 running weird

    My 8403 has been running weird lately. When I start it, it runs good, but slowly loses RPM, then slowly regains its speed. I know the carb is good because I just cleaned it, including the jets and passages. I thought it might be a plugged muffler and clogged exhaust port, but I just replaced the muffler with an NOS cast one, and I cleaned the exhaust port while I had it off. I'm wondering if it needs a new ring and piston. It's a 1984 model, so it''s possible that 35 years of use has taken its toll. Did the F Series engine cylinders have nikasil? On that note, has anyone ever used a ring and piston kit from Ebay, or is there a better one out there?
    Lawn Boy 8403
    John Deere 14SB
    John Deere 116
    Stihl KM 90 R Kombi System
    Stihl HS 81 R Hedge Trimmer
    Stihl MS 260 Pro
    Still MS 261C

  2. #2

    Join Date
    Jul 2013
    Posts
    650
    Location
    Michigan
    Mower
    Kubota, Lawnboys (5), Toro/Suzuki's (2), Honda HR17

    Re: 8403 running weird

    Hello,

    No Nikasil.

    Have you done a compression test? Cleaning the exhaust port should be done with a wooden dowel as anything else may damage the cylinder wall, piston or rings. The loose particles of carbon can cause cylinder damage too.

    AS far as I know the cylinder jug and piston are not available anymore (although eBay may have NOS parts).

    I think one guy on this forum, put a new piston in a F engine and the compression wasn't raised substantially.

    Regards

    Jeff
    Last edited by jp1961; 07-14-2019 at 11:07 AM.

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