[dhgeyer]

Does the bike start easily after sitting overnight with the choke lever in the OFF position? It shouldn't, even if the throttle is part way on. If it does, then the choke would be a good place to look.

The choke cable enters the carburetor on the left side, high up, at the front. There's a brass nut, and the cable goes through an elbow right before going into the carb. If the elbow got pulled out, it could get stuck, and that would cause the choke to be on. Also, the choke cable has an adjustment up near the choke lever. If the locknut came loose and the adjustment moved, that could cause the choke to be on.

If the bike doesn't start easily, cold, with the choke OFF, your problem probably lies elsewhere, very likely one of Easy Rider's tests might find the problem.

The white knob you mention is indeed the idle adjustment, but it's very unlikely to have moved by itself, and just turning the idle down using that would be a "Band Aid" solution, and probably not good for the engine.

Another possibility is something sticking inside the carb itself. Has the bike been sitting for a while? Doesn't seem to take long for these carburetors to gum up.