Aftermarket Pipes Backfire

Our Friends at SuperTrapp had this to say:
Do aftermarket pipes backfire? A backfire or “lean misfire” on deceleration is primarily attributed to an improperly tuned engine. Under this circumstance, the low speed fuel circuit needs to be adjusted. On a street bike, the rule of thumb is to adjust the fuel mixture screw out in ½ turn increments to add fuel. If you reach 3.5 turns out and it still pops on decel then go up one size on the pilot jet and turn the fuel mixture screw back to one turn out from bottomed.

Repeat this process until the misfire is eliminated. In some cases, this problem is an indication that the exhaust is too free flowing (ie. Head pipes too large in diameter or muffler core is too large) for the motor configuration you have. As always, check your spark plugs to verify the tune is correct. The plugs should be a light tan in color if tuned properly. If the exhaust is too “free flowing” you will ultimately add too much fuel which will cause an excessively rich condition and foul the plugs.


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