I haven't enough experience with the PulsaPrime to go straight to a solution, Mark. Like the PulsaJet it just pumps fuel into the small well in the top of the tank so that it overflows continually back into the tank, and the thick tower with the main jet in the bottom (or the side near the bottom) sucks fuel up from the well due to venturi suction. Hence there isn't much that can make it go very rich other than actual internal damage to the carburetor. Since all of the fuel that goes into the venturi is supposed to have to go through the main jet, it may be a blocked return from the well to the tank (the return is just a big hole in the side of the well), a damaged main jet, leakage through the primer pump directly into the venturi, or some other damage that allows fuel to bypass the main jet. That is why Joe suggested a leak across the diaphragm, from the fuel pump to the area that is subject to venturi suction. On the PulsaJet that kind of leakage could happen very easily, but the PulsaPrime is much less subject to it. If you can disconnect the primer somehow, you can see whether it is leaking through to its discharge side. That primer is a bit tin-pot and AFAIK is the most common source of problems with that carburetor, though not usually by making it go rich.
