Fuel usually isn't a cause for bucking, it's usually ignition. Check the wire that goes from the coil to the points. Where it runs under the points plate, they can get chafed and short out intermittently when vacuum advance moves the plate.
Problem solved (at least it appears to be)! Thanks to everyone for their input, especially Ross. I looked at the wire from the points to the coil, which although not chafed was loose to the point where I could pull it away from the points with my fingers. It had contact, but I'm guessing when the vacuum advanced the timing it would move the points away from the wire breaking the connection and then reconnect when timing retarded. I wouldn't have looked there without all of your input.