Need Help with 215

I am having issues with my '53 F-350 with 215 ci 6-cylinder. The engine stumbles greatly off of idle, you can hear it sucking in air through the carb . You have to feather the gas, or have the choke pulled out, or have the truck running at 1200 rpm for it to get the through the stumble. I've tried adjusting the timing and I've also adjusted the air/fuel mixture screw both in and out, but it still stumbles. I've also looked for vacuum leaks at intake and carb base, but couldn't find one Any ideas?? Thanks.
Rusty

Have you checked the timing at the varying RPM's as mapped out in the specs? kind of sounds like you may be having a problem with the LOM. Also you may try changing the acceleration pump rod to the other hole.

Fred

Check to make sure your accelerator pump is working. This sounds like a classic case of a no-working accelerator pump.

-Fred