If I'm remembering rightly, the Walbro WDA has an internal fuel pump and shouldn't require an outside pulse pump. If the internal pump is bad or partially plugged, the extra pump may not be sufficient to push fuel through it and supply the engine at more than an idle. You may want to put a kit in the WDA and do away with the extra pump, or better yet, swap the Walbro out with a Mikuni VM 34 or 36 and have far fewer problems.
Good Luck!
Stuck in the seventies- not in the swamp.
(6) Attex, a Hustler, a Super Swamp Fox, (2) Tricarts, (3) Tri-sports, a Sno-co trike, 3 Dunecycles, and a Starcraft! ...so far