Here's a trick I learned about ST engines from a guy at our field.

Put an inline fuel filter in the PRESSURE line; between the muffler and the tank.

Seems the ST carbs are very touchy and don't like dirt in the needle. It is possible for soot from the muffler to wind up in the tank, and then eventually into the carb. This is why, sometimes you can crank out, or in on the needle with no apparent engine response. Muffler soot stuck in the needle.

The filter in the pressure line has cured this problem for me.

I own a G90, a 2500, and a 3000. I use this filter in all of them. Works great. Pull it out once in awhile and blow fuel backwards through it too clean. Reassemble and fly away with a big grin on your face.

I need parts for my 3000. Looks like they might be coming down the pipe fairly soon now. I can't wait to get that baby fired up again. It's mounted on a H9 PT-19 1/4 scale. Nice vertical , but not very scale-like.