Doesn't sound like anything to worry about to me. I think it's flickering because the pump is sufficient for the job. The seat opens, the pressure drops, it closes and it spikes back up. Dead head regs do that. I've got a Magnafuel 500 with 12 to 10 to 4 -6 lines and it flickers around too, even with air bleeders back to the tank, and it does it idling or at wot, just faster at wot. If it were steady and dropping I'd worry about that, because it'll only be steady while the seats are open or completely shut. Oil filled gauges or isolated gauges look steady because of the snubbing effect they have. A dry gauge close to the carb, or on the reg reads totally different than the others.