Hoping that the air bubbles have gone away enough. One thing that no-one has picked up too well is fuel foaming in the tank. If you have hard mounted the tank (i.e. not installed it with a foam wrapper) then the vibration of the engine can cause the fule to foam so much that the engine pulls as much air as fuel. You can also get foaming from the clunk and some people advocate wrapping the clunk in foam too but I have never seen that problem myself.

If you are struggling with setting up the carb then nitro in the fuel will make the engine less sensitive to the adjustments being slightly off. It might also be worth investing in a new plug, I would go for something fairly hot like an Enya No3.

I wouldn't go for a new engine if I were you, I think you need to get experience on how to set up an engine and how to install a sound fuel system...