Good info Spec. I agree, did you remove the cover to open the screw?
The plug must be removed to access the fuel screw.
On a stock engine, I'd start at 1.75 turns out, but . . . that's just ME!
Regardless, your bike should start with choke only applied, regardless of pilot (idle) circuit condition and fuel screw adjustment, IMHO.
When you throw the choke lever ON, you withdraw a plunger from an orifice in the carburetor, sumultaneously opening an air passage. Fuel flows from the opened orifice and mixes with the air from the opened passage, this fuel-rich air/fuel mixture is ingested into the venturi for starting the engine.
If your engine doesn't start on choke, I'd suggest you check your choke (i.e., "starting enricher") system--is the plastic cap holding the choke cable onto the carburetor body intact? Adequately threaded onto the carb body? When you manipulate the choke lever, does the plunger seat fully when OFF and retract sufficiently when ON?
Here's a diagram of the "choke" (starting enricher); vertical arrows represent air, little dots, fuel:
This circuit is separate from the pilot (idle) circuit. Not saying your fuel screw doesn't need adjusting, or that the pilot circuit passage is not obstructed, only--a functioning choke (starting enricher) oughta get your bike kicked off.
EDIT: Both images in this post come from the link Spec provided above ( http://www.gadgetjq.com/keihin_carb.htm