For those who weren't able to free it up any other way...
I had a carb that seemed like it was welded shut i actually bent the brass trying to open it... need a new carb now, but was trying out different things anyways... what finally worked on the engine that had been run once and the plane crashed and then sat on a shelf for almost 20 years was paint brush thinner. The good thing is get one that is approved for nylon brushes and it won't "eat" your rubber/plastic. probably a good idea to remove it first, but anyway. get a container that you can soak the carb in if it isn't free in 20 minutes leave it over night. if it isn't free by then it IS welded shut anyway i know you already got yourself fixed, but though i would help some of the other people out there in RCU land