Holey 4150 Primary Accelerator pump problems
 

So I have been trouble shooting an issue with my 272 in which it backfires when reving the motor. I have isolated the issue is with the primary accelerator pump. The lever on the side which activates the pump wasn't able to move. So thought I needed to rebuild the pump. Well after rebuilding the pump, I'm still have the same issue. The pump works fine while no gas is in the bowl but once it fills up I can't move the lever. So this has lead me to think something is clogged not allowing the gas out. My question is how does the gas come out of the primary pump. When I take the pump apart I see a small hole on the one side is this the location that the gas come in or out. Is there any type of valve or can I just run a small wire threw the hole to clean it up?

I see plenty of videos online talking about the secondary accelerator pump but not many on the primary.

The issue was the needle under the jet was stuck. Simple cleaning resolved the issue. Took the jet out, the needle out, dropped the accelerator pump. the small hole on the right side I cleaned out with carb. cleaner and also blew it out with an air house.

I found this exploded diagram which helped me out.
http://store.boxwrench.net/Holley-Do...ster_p_34.html

Glad you found the issue..thats what I was going to suggest!