Good advise all. Personally I change one thing at a time until I get the performance I am looking for. Usually the easiest thing like the plug or the fuel. If it will run on FAI fuel heck why not. If you don't want to have to change the fuel screw in a colder plug. I am having the opposte problem in regards to propeller size with the SIG Aviastar .46 I just got. When I try to run a small prop it will detonate, must be something to do with the cylinder filling dynamics. It will turn a 12X5 prop to 11,600 on the same setup without a hit of detonation but a 9X6 is crackly.