I am a little confused as to the ""issues" so many seem to be having?? I ran my GRP 21 with a GRP 4 plug, 9853 pipe, 30% fuel, and added one thin copper shim (just to ease the compression a little). It was a raped ape..came off the track at 200 tops, 10 minute runtimes, and it never once flamed out. A buddy of mine is running his without the extra shim, a P3, 30%, and a 9853 pipe and has not had any issues in 4 gallons. If you are flaming out the LSN is too rich and or your plug is too cold...the GRP 6 is way too cold imo...try a GRP4, and tune the engine with the LSN (like noted earlier)..it likes a leaner LSN and a slightly richer HSN...I have run RB's, Novas, Ninjas, Max Power, and Vspecs, and the GRP is likely my favorite mill out of them all.