"Surging" in gear with brakes on at stoplight...

I'll toss my opinion in with those that point to a carb issue; whether it be the vacuum signal to the carb, or a powervalve issue, or a problem in the synchronizing of the fuel coming from the Transfer Slots versus from the Idle discharge ports, or the IABS/emulsion tubes, or even the wet fuel-level.
But above all, the timing better be stable