Starts to run slow then fast for a minute after it gets warmed up then dies & backfires like a gunshot after it is no longer running.

Also, brand new battery and will only start if jumped from my car. New carb on it, good plugs. Just crazy power fluctuations when warmed up like someone is moving the throttle back and forth.

Hi,
Sounds as if you have things complicated by the fact that you have multiple problems. I would say that you have an air leak in the intake and probably a blown head gasket on one side and possibly a compromised one on the other. Did you go back with the correct plug type?
Peace,
Clarke