Thank you Mike, Shoprat, Pro70, Jerry, Pat & Gassersrule, Then I think this is why my motor is backfiring at high RPM's. I've been overwinding it. I looked at the paperwork that came with my motor & redline is 6000 RPM. I've been winding it over 6000. I'm sending away tonight for a 6000 chip for my rev-limiter. I don't think it's running too lean cuz the motor was professionally built & tunned. And the guy who put the motor in set the fuel pressure regulator at what he said was the right pressure {6 pounds?}. It also backfires when I'm turning it over to start it but not once it's running {at lower RPM's}. So maybe the timming is also off? In fact, I think I read where blower motors should start in an instant. Why does mine turn over & over? Thanks again! Bill