I was running 10% SIG 25% castor fuel in my CL combat plane with the BigMig25 on the nose with no problems. My last match though my pitman got a syringe of 35% in the bladder by accident. Now I know you figure you'd wonder what was up when you had to adjust the needle after 3 matches of not touching it, but I was in a rush but MAN did that engine scream, up till I centerpunched the other guy. If you are blowing plugs, add head shims or back off on the nitro, but there is lots of power out of normal fuel so you don't have to buy more expensive, less you want to.