on the Holley Webber, no I personaly don't have any experience with them. However I have only ever had two things sound like you describe, one is fuel starvation (as, in my case, a filter plugged up) or the plug gaps geing way too wide (in a relation of mine's daily, because it had been 80+K since the plugs had been out). So I would go with fuel starvation with your descriprion.
Could there be water in the fuel causing this?
Hope it's a simple fix (like an inlet fitting filter, as opposed to a full tear down of the carb).
Good luck.
