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rotorwrench · 11-10-2019, 10:34 AM

Popping in the exhaust takes both unburned fuel and fresh air in order to happen. Most of the time it's a leaky exhaust that allows fresh air to leak in as was already mentioned. changing the mixture will affect the combustion process more that what happens in the exhaust. When you let off the throttle the fuel mixture drops of with the closing of the throttle plate but the idle mix portion is still there. A leaky exhaust valve or valves can do the same thing by allowing fresh air into the exhaust.

Harley Davidson motorcycles had problems with this but it was aided by the way the ignition system functioned. They used a dual coil that fired both plugs every time the breaker points opened. Folks also used short open exhaust systems a lot so that didn't help either.

11-10-2019, 10:34 AM	#11
rotorwrench Senior Member Join Date: Jun 2010 Location: San Antonio, Texas Posts: 16,436	Re: Backfire or popping when going down hill Popping in the exhaust takes both unburned fuel and fresh air in order to happen. Most of the time it's a leaky exhaust that allows fresh air to leak in as was already mentioned. changing the mixture will affect the combustion process more that what happens in the exhaust. When you let off the throttle the fuel mixture drops of with the closing of the throttle plate but the idle mix portion is still there. A leaky exhaust valve or valves can do the same thing by allowing fresh air into the exhaust. Harley Davidson motorcycles had problems with this but it was aided by the way the ignition system functioned. They used a dual coil that fired both plugs every time the breaker points opened. Folks also used short open exhaust systems a lot so that didn't help either.