Mark,
You must me running with no air cleaner. Carburetors do make a sucking sound, but using the sound as a diagnostic tool isn't very reliable. A malfunctioning accelerator pump usually won't allow the engine to spin up at all, and is accompanied by bucking and backfiring.
I would check the timing again...this is usually the item that will affect performance the most. Run as much advance as you can without any negative side effects.
Have you set the valves recently? This can affect how snappy the rig is too. If you have a timing light, disconnect your vacuum advance and plug it at the carburetor, rev the engine as you watch the timing marks..your mechanical advance should make the timing marks walk forward as you do this.
Fiddle around, but I wouldn't fixate on the carburetor before I did some timing work, and checked valve lash.
Stuart
