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308 backfiring

Discussion in '308/328' started by decardona, Aug 1, 2005.

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  1. decardona

    decardona Formula 3

    Apr 23, 2005
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    PA
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    Dennis Cardona
    #1 decardona, Aug 1, 2005
    Help, after using resources found here on Fchat, (thanks Birdman) I synched the carbs on my 308. While going thru the procedure, I was able to get everything dialed in and the car ran beautifully. Well, the next time I took the car out, it started backfiring when coming off the gas after high revs. Going up thru the gears is no problem. And it has plenty of pull in every gear. But, when you downshift, or drop the car into neutral, it will backfire loudly. It did backfire once while I was synching, but with all the adjustments it didn't do it again. I'm guessing I need to lean out the carb from which the backfiring is coming from, but I figured I would ask those who have dealt with the problem. Please, anyone, let me know if my thoughts are correct or if I need to go in a different direction. Thank you in advance.
     
  2. BillyD

    BillyD Formula 3
    Silver Subscribed

    Feb 28, 2004
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    Bill
    #2 BillyD, Aug 1, 2005
    Any leaks in exhaust system at all? Recent spark plugs? & are they burning clean?
    Bill
     
  3. FasterIsBetter

    FasterIsBetter F1 Veteran

    Jul 22, 2004
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    Steve W.
    #3 FasterIsBetter, Aug 1, 2005
    Backfiring when coming off the gas can be a symptom of running too lean. You might want to check your mixture. I had a similar problem with my Mondial, and it turned out to be broken baffles in the muffler causing no back pressure. But in your case, since it happened coincident with tuning the carbs, I'd start there. (Old rule of auto repair -- if a new problem arises immediatly after a repair, look to the last thing you fixed and figure out what you did wrong.)
     
  4. Doug

    Doug Formula 3

    Nov 13, 2003
    1,473
    Louisville KY
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    Doug
    #4 Doug, Aug 1, 2005
    Sorry for the laymans terms but I had the same on my GT4 and I don't feel like digging up the manuals for the exact term. Try turning out the screw(counterclockwise) on each carb at the lower part that sits facing the cars rear on each one. They go in at an angle. Start with 1/4 turn for each and take a drive that heats up your exhaust system. The pass side front inner one is hard to get without the airbox off.
     
  5. decardona

    decardona Formula 3

    Apr 23, 2005
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    Dennis Cardona
    #5 decardona, Aug 2, 2005
    Thanks for the input. Plugs are new and burning clean. I did notice a small rust spot or hole near where the exhaust pipes are mounted. If trying to enrich the mixture doesn't work, I guess I will have to look into a new muffler/exhaust.
     

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