Accelerator pumps mess with the opening of the throttle, not closing. When you close the throttle, the vacuum goes way up, so the vacuum advance should pull all the way in. When you open the throttle, the vacuum drops to near zero (depending on how quickly it's opened) so the vacuum advance returns to home position. The accelerator pump also operates when opening the throttle, without it, the engine runs lean for a split second till the air flow and fuel flow come back together. You should see fuel spray about anytime you open the throttle. With a quick stab, it should really spray, a slow open might just dribble out, but either way, you should see some fuel.
Since it's acting up opening and closing, look to the distributor and timing. Dwell meters are cheap, no need for Snap-on here!
Joe
