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On 28 Feb 98 at 1:18, Soap Duck wrote: > Since I have got my carb put on it has been doing a little bit of backfiring. > I know not why. However, I do know that there are no vacuum leaks. Could it > perhaps be the wrong amount of Fuel/air mixture? Would bigger jets on the > carb solve this? If it helps I think I have a few exhast leaks. Backfire usually occurs under deceleration and is caused by the under-rich mixture which usually fails to burn in the combustion chamber being passed on into the exhaust where the gas condenses out and waits for a source of ignition (a bit of hot carbon, or expelled hot gasses from a combustion cycle that fired.) There is not a lot you can do for this unless it is happening in normal operation (not under deceleration.) If it is happening under acceleration or cruising, then your mixture is wrong, usually too lean. If it is happening under deceleration then the best you can do is make sure your throttle valve is closing completely when you let up on the pedal. There is no truth to the common belief that exhaust leaks can cause backfireing since it is clear that the positive pressure in the exhaust means that any leak will be from the inside out rather than the other way around. True backfires, meaning firing backwards through the intake manifold, are rare, and are usually the result of grossly misadjusted valve timing or burned intake valves, neither of which happens in air cooled VWs.. Jim - ******************************* Jim Adney, jadney@vwtype3.org Madison, Wisconsin, USA *******************************