Thanks all. First let me answer the questions:
    1. This is a Type B downdraft carburetor (not asked, but relevant).
    2. I have not plugged the vacuum inlet at the manifold, only at the end of the hose that plugs into the wiper motor.
    3. I don't believe my fuel pump is a wiper pump; there's a separate motor with a switch (if I've understood your question).
    4. Choke is not stuck closed, because I must manually open / close it from under the hood (another topic for another thread), and I always remember to open it after starting.
    5. Air cleaner is the large, original oil bath with horse hair filter element (or whatever that material is).
    6. Air cleaner could be plugged, I suppose. Haven't inspected it lately.
    7. This is a 3-speed, on the tree.
    8. There are no new drivetrain components; this thing is 98% original. I've possessed it for 10 years, it's been in the family for 50 years. My mom's husband did some work on it 15 years ago, but it was mostly trim, maybe some front suspension.

  • What I plan to do:
      1. Plug the vacuum inlet at the manifold and adjust the idle mixture and idle speed to 450-500 rpm. (I don't have a tach, so not sure how to know the rpm).
      2. If that doesn't help, I'll adjust the timing. I've never done that before, but I know the procedure has been written about abundantly on this site.
      3. If that doesn't help, I'll remove, disassemble, inspect and clean the carb, with emphasis on the idle system.
      4. In any case, and maybe as a matter of safety, read the service manual section on motor mounts and inspect them.

    • Thanks all. I'll keep you posted. Any more info and suggestions are appreciated.

DJ
'51 Chevy 3104 1/2-ton 216