I think neither; There's a slim chance that the fuel level is a tad low. But
I think you need to put the throttle blades a little further up on the transfer slots
To me it sounds like the throttles are closing to far too fast and a momentary leanness as the mixture screws are forced to take up the slack. You may have to back off the idle-timing if the rpm goes too high, and that would require a revisit to the power timing.
