I have a GMS .46 in a Sky Raider II that I broke in well and have flown about 5 times. It's been a great engine right from the start. It's run very strong and has always started with no ore than a single bump of the starter. Just lately, it has begun to just stop running. It starts and runs well then just stops taxing to the runway or halfway into my takeoff run. Sometimes it will run for a minute or two in the pits and die abruptly. It always restarts right away but the problem repeats. I've tried to run it lean to rich and everywhere in between, same result. I've flushed out the fuel tank and all other tubing. I've cleaned the high speed needle valve and flushed the carb. The tank is isolated well in foam. I'm using 15% Omega and an OS #8 plug. Any advice?