Re: Too much fuel, not enough air.
To lean the mixture in a stock chinagirl NT carb, move the needle circlip higher on the needle. This lowers the needle at any given setting and allows less fuel into the engine.
Lowering the clip on the needle richens the mixture, raising it leans the mixture.
If it's still too rich with the needle in the top slot, buy a smaller main jet.
If the engine runs great everywhere but four-strokes at full throttle, buy a smaller main jet.
Most of my china girl engines like the needle circlip in the second slot from the top with the stock exhaust.
If more is better, then too much is just enough.
If you can't afford it, build it yourself.