My 2007 america backfired regularly on startup for a couple of years, and almost every time for the last year but so far everything has held together. Strangely though the battery needed to be replaced about two months ago ( 8 years old ) and it hasnt backfired since...work that out..? I have heard that latter models,if you can call 2007 a latter model, were stronger in this area, dont know for sure though.
