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Thread: 1940 chief backfires

  1. #1

    Default 1940 chief backfires

    My 1940 chief will backfire thru the exhaust when letting off on the throttle usually going down a hill ,I tried adjusting the high speed needle on the carb but it does not make too much difference. The motor has about 2500 miles since rebuild.any ideas what I should try next thanks jerry

  2. #2


    The slightest exhaust leak where the pipe enters the cylinder will cause this to happen. Most cylinder ports are worn and unless you want to bore it out and expand the pipe you will probably have to live with it.


  3. #3
    Join Date
    Jan 2008
    S.E.N.Y. State American side of Hudson River


    When I purchased my 48 with car from Al Ceccini, he told me for fun when going downhill using the engine as braking, retard the spark and you will get a series of pretty loud backfires. Well, I tried it and you sure do. Check your timing also.
    D. A. Bagin #3166 AKA Panheadzz 440 48chief W/sidecar 57fl 57flh 58fl 66m-50 68flh 70xlh

  4. #4
    Join Date
    Aug 2009
    rural eastern South Dakota


    I've been enjoying that cackle for 27 years, solo and sidecar. Can't tell you what it hurts, if anything. Scares little leashed doggies pretty bad. Bad dog or bad bike?

  5. #5
    Join Date
    Jul 2010


    Quote Originally Posted by fillibuster View Post
    Scares little leashed doggies pretty bad.
    Also works for bicycle riders going side-by-side, they usually get into single file if I back off the throttle quickly and create a backfire.

    I've noticed the backfiring is worse some times than others, and I think it's weather related. But being the lazy type, I have a good "sweet spot" in my carburetor so I don't wander too may clicks off of that when it gets colder or hotter or more humid, so the end result is some days I don't hear anything while other days it's downright embarrassing.
    Pisten Bulley is Harry Roberts in Vermont.

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