That choke has a vacuum assist piston which has a habit of getting gummed up and preventing the choke blade from moving. It's an easy fix- - - -after taking the choke cover off (and replacing it with a correct bimetal spring cover if possible) soak the piston and its associated linkage with spray carburetor cleaner, and gently work the linkage back and forth until things free up. Another problem is with the choke heater tubing. It was supposed to draw air through a tube that passes through the exhaust manifold. The tube can rust out and allow exhaust gas, not clean air, to enter the choke housing. That causes carbon buildup and sticky parts. The fix for that is to plug off the passage in the exhaust manifold and wrap a few turns of copper tubing around the exhaust pipe to provide the choke with clean hot air.
It's also possible to adapt an electric-heated choke cover from a later model Rochester carb and eliminate the hot air pipe altogether, but it takes some tinkering and modifying to make it work.
Jerry
