I notice that when I put my spark arrestor on I start getting this popping backiring noise when I let off the throttle. IS this normal? Am I supposed to change my jetting or change the richness of my fuel screw?? Also when letting off the throttle the rev's stay high sometimes and sometimes they come back down to normal. Have had overheating issues once because of this. Anyone know why the engine doesn't drop back down to idling RPM??