It's not the fuel that's causing your grief.

It's the CARB. PERIOD!!!!!

I know. I have 2 big cats. A ST2500 and a ST3000.

I have run different fuels in both of them at different times. This was before I broke down and listened to the guys who told me too buy the OS 7D carb. You see; I'm stubborn. I was convinced that I could get the engines to run, if I would just tweek the needles the right way, or if I tried a new fuel, or if I tried a new plug, or a different plug, or a different fuel.

ALL BULLS**T!!!!!!!!

I finally got tired of fighting it and went out and bought two brand new OS 7D carbs. My problems went away faster than a fart in a hurricane. And I'm not lying or pulling your leg.

One other thing to consider: If you have the engine mounted inverted, your going to have problems. The engine will never idle well and it will burp, fart, wheeze, cough, and gurgle on transition. Try adding on-board glow, if you must mount it inverted. Or mount the engine just slightly off-center. This will move the glow plug away from the bottom and prevent fuel from "pooling" up around the plug and drowning the engine. With the engine mounted inverted, the plug is dead center on the bottom of the head, and it becomes flooded and cools off quickly. This causes the burping and farting and often the dreaded deadstick on final approach.

I am currently running Omega (pink) 5% fuel in the ST2500. It runs just fine. It turns an APC 16-8 at 8300 RPM. And I fly at exactly 5973' above sea level, where the air is thin. Engines lose about 15-20% power at this altitude.

I am running Cool Power (green) 15% in the ST3000. It runs just fine. It turns a Zinger 18-8 wide blade at 8600RPM and a Zinger 20-6 at 8000-8100RPM. Sometimes I will run Cool Power 10% if the LHS is out of the 15%. The engine doesn't run any different.

And by the way: Higher nitro makes the engine run COOLER. Not hotter, as most people think. I have put a temperature sensor on the head and the glow plug, and measured temperatures with different fuels.

Nitro is kinda like the octane that is in the gas you run in your car. Higher nitro, or octane, makes the fuel burn SLOWER; therefore creating a longer burn on the compression stroke. This makes the actual combustion process cooler; because it burns in a larger space. It burns in the entire cylinder, rather than just in the top of the head. This lowers the pressure of the explosion, which lowers the heat.

The reason that higher nitro gives you more power, is because it does burn longer. It produces the power slower, but more consistantly and for a longer period of time on each stroke.

Just get an OS carb. or another suitable replacement, and you will be happy.

Hope this helps.