Carb- what is this screw for?

[SeanPaintsFlames]

250 inline six- I rebuilt the carburetor a few months ago, it runs kinda junky, so I went to take the carb off and mess with it, but noticed that this screw was loose. So, I went to tighten it up, but it kept going and going like it's an adjustment of some sort. Accelerator pump? The truck has really crummy off-idle response, and I figured it was flooding, but the floats are right where they're supposed to be. Whereabouts should this screw be adjusted?

[j.kirn]

that is the adjuster for accelarator pump. i couldnt tell you the correct adjustment though sorry

[fleetsidelarry]

I haven't owned anything with a 1 barrel carb in ages, but I was curious so I looked in my '63 shop manual, that looks like a model "b" carb. If so, according to the manual, the screw is an idle vent and should be adjusted (by turning the screw) to be open .050" at regular idle position (low step of fast idle cam, choke open)