Hate to hear you're having problems.
Before tossing in the towel, check a couple things with the carb that are simple but can cause problems if not done correctly.
1. The bowl (cup) is very specific as to it's placement. there is an angled portion and across from that a dimple. The tallest portion of the bowl (dimple is at the "center of the tall area") is for the float to be able to pivot up into without binding. You have to make sure that the hinged portion of the float is 180 degrees opposite the tall flat with the dimple when you install the bowl.
2. The little thin wire clip that holds the float needle needs to go through the hangar on the float in a specific direction. check the rebuild manual to make sure it's going in the right direction. Off hand i can't tell you if the open end is supposed to point to the air filter side or the intake pipe side, but it does matter.
Either of those two items can hang the float up albeit in different locations. If it hangs "up", it will run til the bowl empties and the stuck float is preventing fuel from coming in so it will cut out. Stuck down and it'll overfill. I don't think you need to buy a carb. If you check the two items above and it still doesn't work, e-bay the engine and stick a harbor freight etc. clone in it. Just make sure you buy one with the correct shaft diameter--the keyed portion of the shaft length will likely be a little shorter on the clone, but that's a non-issue.
As far as the lock-up goes, no idea, but it may not be the internals, could be something jammed up in the flywheel area.
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