What can be wrong with old 2 cylinder craftsman lawn tractor mower will not start with choke pulled have to cover carburetor with your hand?

Apparently, the choke linkage needs adjusting. Easiest way to determine is by removing the air filter and then pulling the choke control all the way and looking into the carburetor to see if the choke baffle is closed completely. If adjustment is needed, leave the choke on and loosen the cable hold-down screw; pull the cable back to where the choke baffle is completely closed, then re-tighten the hold-down screw.