Carter rebuild kit?

If your floats are too high, the fuel sloshes around, and dumps into the main barrels causing flooding and all-around wierd stuff. The float level actually affects the mixture, to a certain extent. If its too low, the carb will run slightly lean. This is a very fine adjustment, way less than,say, changing jets or rods. Also, if its too low, the accel pump system doesnt work correctly. You wont get a pump shot 'til the throttle is opened some.

There are other factors as well.