I am looking to buy a 2011 Triumph Thruxton, it is a nice bike and I want to make an offer except it has a backfire when shifting down gears and when you release the throttle (coasting). The bike has a 2 year warranty and the guy said the fuel mix is "probably" too rich (or something like that). He said they need to get the mechanic to adjust it. I wanted to know if backfiring can cause long term damage to the motor. I read here (on a different thread) about it but didn't get a definitive yes or no. Should I not worry about the bike because of it?