Recommend service manual, and/or visit to competent shop or consultation with knowledgeable individuals.
Easy to tell whether your carburetor is receiving gasoline: After cranking engine for awhile, open carb drain screw (at bottom of carburetor float bowl, 3 mm Allen (hex) key required on later-model KLR650s) to see if any fuel flows out.
You must crank your engine first, because . . . the petcock is vacuum-operated; engine vacuum must activate petcock for fuel to flow. A vacuum hose connects the petcock to a port on the carburetor.
The "CARB OVERHAUL" and the "CARE AND FEEDING OF THE CVK40" threads elsewhere on this website provide valuable fueling information.