I second the exhaust leak on decel popping, i found my leak to be off the rear header with bad copper oring. mine is first gen tho, now the big black hoses are you carb manifolds at least what i call them, this could be causing a lean condition, possible replace i would replace just because the shape there in, then I would finish that off with a good carb sync and see where you stand there. my bike would also fire right up with just 2 cylinders firing... and yes only 3 cylinders if you dont know these bikes and motors you would never know you was running 3 cylinders but once you get all 4 firing O MY LAND YEEHAW!!!!!