cameron724,

I had a u-can-do 46 with a ST 51 a few years ago. The ST 51 was fine for sport flying but it was not good enough of 3D. I had my ST 51 inverted and used a fueler valve. When I wasn't flying I would keep a spare piece that fits into the fueler valve plugged into the fueler so the fuel wouldn't siffin into the carb. You'll also need to lean the low end on the carb so you'll have a good idle or it will keep dieing on you. I really didn't have any issues running the engine inverted.