Help with ST 90 needle valve sttings
Your engine being inverted is your main problem. Unless you change something, you will fool with this to a pont of selling or junking a perfectly good plane.
Majority of those who invert a 2 stroke leave the fuel tank in its original slot--which is now considerably higher than the carb line.
But just for informational purposes. first, set you throttle opening to its approximate idle position. Open the high end a couple turns. Then close the low end. Disconnect the fuel line from the carb. Attach a spare line to the nipple and (at the same time, blow into the fuel tube and open the lowend until you here a hissing noise), Now your low end is in the ball park.
But as i said earlier I have a couple inverteds and I had to do some cutting to place the tank basically on the floor of the fuselage.
I also have a G90 in a Shoestring. Same engine has been in a couple other planes and is very powerful and reliable.