Merffy on here has the same deal. Only one I have seen, but it might be the alt. compensating pump that I have heard about. It does work similar to a TD pump only with vacuum. There is a pin with a ramp in it.
it has vacuum hooked up to where the vent would be on a TD pump..
maybe as the engine revs go up, it sucks the diaphragm down, and increases fuel?
yep. that is how merffs works. There is a spring and starwheel just like a TD as well. It is kinda different:D