My AFB seems to drop gas from the throttle shaft. It does it with the engine running and with it off. What is the usual cause of this? Are the floats a little high?

Fuel pressure should not be an issue.

It is an older carb. I bought it new in the late 80s. It's seen intermittent use since then.

It sounds more like something is stuck in the needle and seat keeping it from closing.

Check the floats hieghts if it's not the needle and seat

As said check float levels and prob can get needle/seats seperate & I would check the idle psi, most vac gauges have a psi side & come w the black neoprene adapter about the size of your thumb that slips over the male inverted flare fitting on your fuel line you unscrew from the carb inlet EDIT & a good filter

this is prob very remote but I had one that had a pinhole in 1 float, gas would drain out when you had carb apart, then when re-installed it would idle fine for a couple minutes and then start loading up at idle, you could hear the difference in just a minute or two. Couldn't see th hole, finally discovered this when I picked up float and felt th slosh inside the float.
Like I said prob remote but something to look for when it's apart, and uh good luck with it

Float level or something in the needle/seat.