TBI fuel delivery problem when starting

I am resto-moding a 69 C10 using a GM 350 TBI engine/700R4 setup. I wired the truck with Painless harnesses including the TBI harness. My problem is starting. It turns over fine, and if I prime the throttle bodies, it starts and runs with the injectors supplying a good stream of fuel. However, if I don't prime them, it won't start and no fuel comes out of the injectors during the start process.

I'm stumped. Anyone have any ideas?