Have you removed/disabled the AI? That's the tube you see next to the sparkplug. It adds air to the exhaust, that popping is unburned fuel burning in the pipe. Do a search on 'AI removal' and you'll find what you need.

BTW, welcome to the Sanitarium.

Steelheart- '03 Speedmaster Black/Yellow The Hayabusa Killa 16" Shorties/140 mains/Airbox drilled Procom CDI "There is no cure for Celibacy. But we can treat the symptoms."