The ST3000 was ported and tuned to give max output at 7900RPM.
Prop it for 7300--7500RPM on the ground and it will unload right into the sweet spot.
I had 2 of the ST3000 engines years ago. Ran them both for gallons and gallons and gallons of fuel. Probably 30 gallons of fuel through just those 2 engines. Got to know them REAL well and how they reacted to nitro, props, plugs, oil, etc.
I always ran Omega 5% fuel in them. The oil content is higher than the ST fual--but oil never hurt an engine and they ran great on the Omega fuel.
These are high compression ringed engines. 5% nitro is plenty. 10% causes detonation unless you want to run a cold plug and shim the head. Just a waste of time and a lesson in beating your head against the wall fussing with it. Just run them on 5% or even FAI 0% fuel with a regular ole plug. Tower plugs work great, as do the OS plugs--but they are just too expensive.
I ran either a Master Airscrew Schimitar 19-8 or a standard Zinger 20-6 and had them running right in the 7300-7500RPM range. Ungawdly thrust and vertical performance on a 12 pound plane.
Don't run it inverted unless you put the tank centerline even with the carb spraybar first. They flood easily at idle when the tank placement isn't perfect. Cline regulators work great on these engines. Perry pumps DON'T. Been there, done that. Wasted a season of flying trying to dial in 2 different Perry pumps and all I did was make myself miserable and practiced my deadsticks.
CLINE CLINE CLINE!! Only way to fly.
Just run a large clunk and large fuel tubing if your going to run it without a regulator. If you get a Cline, medium tubing is fine for the entire system.
Carb problems? Can't make it run, no matter what ya do? Beating your head against a wall? Go get an OS 7D carb or a Perry carb or an ASP carb and you'll be smiling in no time. [sm=thumbs_up.gif]
Good luck. Let me know if I can help.