I have a kx 500 powered outlaw kart with a pvl ignition system. I have been having a hard time to getting it to run right right. It has been progressively getting worse, since i bought the kart, it would run great for half a race and quit, lose power and start to miss. last weekend it ran for a total of three laps, when trying to start it it would just backfire, we have gone through all the wiring checking for a bad ground and have come up with nothing, next up is checking the timing, which i not sure where it is suppose to be set at. If the timing is not out what would you guys recommend looking at next