RE: Official Hyper ST thread!!
I use the OS No. 8 Plug, but I switched my engine out to a picco p3. Still, that plug should work for you. I had all kinds of trouble getting that engine to run correctly (macstar .28). Ran hot no matter how I set the carb and blew out after a gallon. I'll be interested to hear if yours works out. If not, the picco p3 has worked really well for me. I have over three gallons through it and its has great compression and power. The directions for the hyper ST suck by the way. The engine is not even addressed at all in them.