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16hp Briggs I/C backfires

Discussion in 'Mechanic and Repair' started by Poot, Sep 12, 2007.

  1. Poot

    Poot LawnSite Member
    Messages: 24

    Morning. I've a maybe 1988 or 1989 model Briggs 16 hp I/C on a Lincoln welder/generator. I got it with a broken rod so after a thorough rebuild including rings/rod/intake valve AND lapping both valves/setting the stem clearance, it ran great. Earlier this year I used it and during the course of it started to lightly backfire so I adjusted the high speed jet and it stopped this. After shutting it off I noticed gas dripping from the carb. When I got the welder I was also given a BRAND NEW carb with it so to save time I swapped them out and it ran great once again. Yesterday I used it for about an hour and it started backfiring VERY badly. Adjusted the high speed jet and it cleared up...for a while. I discovered if I pulled the choke half on it ran better with an occassional backfire. Then without warning it stopped running but would start right up again. While there COULD be water in the carb, I completely drained the tank and found not a trace of water. I also replaced the plug with no change. It's like the exhaust valve is hanging open sometimes?? Oh, and the bigger reason for changing the carb earlier this year was the original one dripping gas after shutting it off. Now the new carb is dripping gas after shut down. I haven't pulled the flywheel and haven't a clue if it has points or electronic ing. but am guessing it's got points. It's been so long since I've dealt with points that I can't recall if they'd cause one to backfire. If memory serves though I'm thinking not because as they wear the gap closes causing it to just not start. Dunno but hate having to work on something I need to work on something. I have welding to do but have to baby a welder to weld so the job becomes compounded doubling the time involved. Just looking for some ideas before I start my witch hunt.
    Thanks :waving:
  2. Restrorob

    Restrorob LawnSite Fanatic
    Messages: 11,029

    If the new carb has been sat up for a while the float needle valve could have gotten hard causing it not to seal off fuel flow, The float needle valve in the old carb most likely has a groove wore in it causing it not to seal.

    The backfiring could be a valve sticking or the ignition coil heating up causing weak spark. A 88/89 would most likely have electronic ignition so you have no points to deal with.

    Have you performed a compression/leak-down test ?

    Also, You didn't post model and type numbers off the engine......
  3. Bill Kapaun

    Bill Kapaun LawnSite Senior Member
    Messages: 963

    I'm kind of wondering about contaminated fuel.
    Have you changed the fuel filter?
    Leaking carb may be a different issue.

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