I have found that the ST idle needle setting has an effect on the high speed. When I get the idle set properly, I get a very reliable idle with good transition and more top end rpm. You will actually have to fine tune the high speed setting after the adjustment of the low speed needle. Tach your engine at WOT before and after-- if it is as rich as you describe, you should see a BIG increase in the top end when you get it set properly. Do the pinch test on the low speed needle setting as well as the high speed as mentioned previously in this thread.

The ST carb is very critical of tank position. I would also check to see that the glo plug you are using has the correct heat range for the fuel/ nitro content being used. When those are correct, you should have a very good handling engine throughout the rpm range.

turbo