I was running an APC 15X7 on mine. Never hit it with a tach but level full throttle would rip the prop. Fuel was Powermaster 20/20. Properly adjusted any engine should idle as long as you want. I stand by my first suggestion, fuel it up with fresh fuel. If you do and don't see an improvement after adjustments I will buy lunch next race. My guess is you have the needles set more open then what would be considered normal. Tell tale sign that the fuel has moisture.