If it is a Zenith carb, it probably has a VACUUM accelerator pump!
While I dislike the word "never"; one should NEVER pump the footfeed on a vehicle with an updraft carburetor! Guess where the fuel goes? The vacuum accelerator pump prevents this, as it will only function after the engine is started, and manifold vacuum has been established.
A vehicle with an updraft carburetor should ALWAYS be started using the choke.
The Carter BB-1 does have a mechanical accelerator pump, so the onus is on the operator NOT to use it.
Jon.
