91-99 carb questions...

[wex65]

I am experiencing some stumbling when hitting the gas pedal so decided to freshen up the 91-99s on my '37 flathead.

I got the first one back together and whilst looking at the second I noticed some minor differences and wanted to inquire as to whether a missing screw is in fact 'missing' and if so whether it is an issue.

The first carb has no hole (vent hole?) in the top of the float chamber but this second one does. Any reason for this variation? The completed carb in the photos is the first one without hole and I have circled the vent hole in the second carb.

Finally, in the bottom of the float chamber in the first carb there is a tiny screw which appears to be a blanking screw. the hole and thread do exist in the second carb but there is now screw. Is this an issue and if so what symptoms would it cause?

Looking at the photo of the interior of the float bowl it is apparent from staining the fuel level is at the same level as the hole into the pump piston/spring chamber. I assume this is correct? I measured the first float to be 1.35 inches but haven't gotten around to this second one yet.

Many thanks,