The engine builder that did all my machine work has a Blown Hot Rod on Alcohol. His lopes like you are talking about. I asked him what caused it and he said it was the injector. Motors with an injector or hat like a Hilborn can be made to lope like you are referring to with the blip of the throttle pedal. My guess is that the fuel pump/system is a manual bypass style. Blip the throttle more pressure RPM rises then back to low pressure RPM lowers and then it catches itself, pressure jumps up and the whole thing just continues. Hi, low, hi, low thus lopes with that grunt we all love. Pat should be able to elaborate on it more.

Keith...