I had the same problem couple months ago when my friend wanted my truck gone from his barn after 10+ years sitting there. LONG STORY but I'll shorten best I can. She would crank & run on the small amount of gas that I primed carb with but DIE quick. Bought carb from Memphis Equipment w/o upper vacuum pump on top. Hooked er up & primed carb but would not stay running . I had worked fuel pump lever and felt/heard air move before installation, so I knew pump worked. Removed valve cover, removed fuel pump ECCENTRIC off the front of the camshaft sprocket and replaced with NEW one i had on hand. ALSO replaced SPRING (new) and the ROD (new) going down to the fuel pump arm. it looks like a oversize nail . Hooked everything back up an after about 2 or 3 attempts she was a running. Was a good feeling as I'm getting too cranky to fool with" The Beast "much anymore . Hope this might help add another option for you. Good Luck ! TOM