My 07 Hertiage Softail runs great but one day it had a backfire thru the exhaust which I had never heard before. After the backfire when I pulled up to a stop light the engine did not want to idle. Had to continue to keep the rpm's up. Started off and no problem with running and the bike did not backfire again that day. A few days later the same thing happen 1 time but clears up. Anyone know what may cause this backfire issue.