'70 318 BBD falls flat under load

This IS a "rebuilt," right? These things have a HORRID track record, I"m afraid. Hell you might have a main jet that is out of something completely different. But that's what I'm thinking, main jet or the power circuit. Is this the small bore (318) bbd, or the large (360)?

But I'd be really tempted to tear it down and at least check the piston/ rods for free movement. Hell they may have left the spring out!!

For the record, you CAN DRIVE a car with OUT an accelerator pump. They of course can be a ***** to start, and may need a squirt down the carb. I used to know "an old guy" (LOL, now I'm older than he was then) who used to UNHOOK the pump link on long trips!!!