Who would you let rebuild your Holley carb?

It gets fuel if I pump it but not if I don't. This is a fresh engine I am trying to get fired up to break in the cam and set timing. I have to pump it 3 times and hold the throttle 1/4 way open and with a screwdriver in the butterflies before in order for it to fire. It wants to run but the carb is holding it back. If I hold the throttle at 1/2 or more it backfires. It acts like it's starving for fuel the few times it actually ran for a few minutes.