What Causes the Exhaust Pipe to Backfire When Throttling Down a Motorcycle?

[SanHenry]

The main issue is caused by an excessively lean air-fuel mixture. When the mixture is too lean, the motorcycle engine's spark plug cannot ignite the mixture rapidly near the end of the compression stroke. Even after ignition, uneven combustion occurs, and unburned mixture may continue burning in the exhaust pipe, resulting in backfiring ('popping'), overheating, and vibration. Here are solutions for motorcycle exhaust backfiring when throttling down: Revert to the stock exhaust: Although backfiring may still occur with the original exhaust, the catalytic converter and larger muffler minimize the effect. Adjust ECU settings: Increasing fuel supply can slightly raise combustion chamber density and accelerate air-fuel mixture burning. Setting the AFR (Air-Fuel Ratio) to Rich during throttle-down helps. Many aftermarket exhaust manufacturers' official ECU maps use this method to eliminate backfiring and afterfires.