I have a LX172 I bought a few months ago kind of in a basket. The guy I got it from said it quit running and was throwing new parts at it hoping to get it to run. I got it home and replaced the ignitor and wala it started right up. Now the problem is every time I go to start it, it backfires. Actually it's more like a small explosion out the exhaust. Once it starts it runs like a champ, idles fine and mows great. The parts that where replaced were the coil, spark plug, fuel solenoid and of course the ignitor. Any help on this problem would greatly appreciated. Thank you in advance.