Many of us Run the OS with the Pump Rcpilet,with super results..bashin the product while most have had solid running motors does not help Hoverlow.
I have only 25 flights on my engine and am not of much help.Is your pump above the carb? I think it has to be at the same level or lower,but check manual.Sounds like it most likely flooding it.The inverted engine may add to this effect.Maybe post your plumbing diagram here and some can see if something is mixed up.I know I had the vent mixed up and made a mess with fuel everywhere...