Motorcycle Repair: carb backfire, plug wires, good luck

Question
QUESTION: Hi Mike, I have a 92 soft tail with s&s carb 1 to 2 sec after I shut her down I get a backfire out of the carb and my bike will jump forword my thinking is if it was timing it would backfire from the exhaust what should I be looking for thanx

ANSWER: Pull your plugs and let me know what color they are
Mike

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QUESTION: The front is black and the rear looks good its brown.

Answer
I would test the coil and plug wires to make sure they are good. One wire or one side of the coil might be weak. Also, I would check the timing. If you are to retarted in the timing, the bike will run hotter and cause the problem you describe
Good luck and happy riding
Mike