Its kinda two topics in one but these are the problems I face today...I looked under my car and found my new mini starters teeth are getting kinda chewed up against my flexplate it doesn't ring or stay engaged but iwas wondering if jus needs another shim already got two shims in or if its normal for the teeth to get kinda beat up....everything is bran new on and in engine jus broke in cam yesterday....other question when I rev the engine up it backfires sometimes the car has no exhaust on it jus open headers does it jus need some back pressure or could it be something else???.....other than that new engine sounds great....