To the OP, first, the size of the motor has nothing to do with being able to tune your carb. Either you know how a carb works, or you don't. Just say it. Its fine, We're here to help.
What folks have said about the throttle blades and T-slots is generally correct and could be part or most of the problem, but does not answer why the throttle need to be open so far.
Probably the first thing you should check is the carb fuel levels, and that fuel is not coming out any of the boosters at idle.