today i was delivering pizzas my bike, (big red) with a new 66cc RAW kit, and i turned it off, then it backfired! i first thought it was something that blew off of my block or something, but i stop to inspect and everything was there. then at my next stop,it did it again. i finally at the next stop, i took out my earbuds, to hear clearly, and i confirmed it. is this normal?