If the float height is set causing the fuel level to be too low in the bowl, it may suck air and cause a too lean condition. If fuel level is too low, excess vibration and motion causes the fuel to bubble up/foam which could cause a too lean condition, but normally will push down on the float making it add more fuel.
If float height is set causing fuel level to be too high in the bowl, you should have some leakage out of the overflow lines if you lean the bike over slightest from vertical. Also, you should be able to see the fuel in carb "barrel" and in the airbox.
If the float is too high you will get poor bottom end power, bogging and stalling ( too rich ). The reason is the fuel is being forced up the jets into the carb "barrel" by gravity, because the overflow lines are usually higher than the "barrel" of the carb. That's why when the fuel is left on and the float valve sticks open, sometimes your airbox and crankcase will fill with fuel before the fuel will start running out the overflows.
If the screw with the spring around it is the one you are talking about, that is the idle screw. If it is all the way in ( raising the slide up ), then you are proabably too rich. Also make sure your air filter is clean since that will mimic too rich ( no enough air flow ).
The mixture screw is between the carb and the airbox, it adjusts how much air is mixed in the idle to 1/4 circuit. If the mixture screw is between the carb and reeds, then it adjusts the amount of fuel added. If you have the screw all the way in ( between carb and airbox ), that would make it richer ( less air added ). If it is 4 turns out from fully closed, that generally means you need to go to a smaller pilot jet.... but get the float adjusted first ! ! ! A 50 pilot is pretty small though, even at sea level. Make sure the mixture screw is around 2 turns out from fully closed.
I am not an expert, but I hope this sparks some thoughts on "real world" gearheads and their bikes.
Sly
