wont start

I have a 97400. It was loading up with fuel an running very bad so I rebuilt the carb. When I put the carb back on it started right up without a problem. While I was letting it warm up so I could go for a ride it stalled, an hasnt run since. When I tried to start it fuel was leaking out of the overflow tube. I dont know why the float was sticking but I took it apart and cleaned it out again. Its not doing that anymore but its backfireing through the carb, hard enough to pop the carb of the manifold. It has good spark,and is geting fuel. Any help would be apreciated.