Engine stumble and cut out

[Pat70Z]

I need to reach out for some help. I purchased a Holley 4555 last Spring to use on my stock 70 Z28. It needed rebuild. It now has the following:
- Accelerator pump at .015"
- 8.5 Power valves Primary and secondary
- primary jets 72; Secondary jets 76
- #25 squirter
- Float level at the bottom of the sight hole.

The engine will start and run; but will stumble or quit intermittently. It acts like it just runs out of gas. I can catch it if I pump the accelerator. I replaced the fuel pump, fuel filters, power valves. I checked for external vacuum leaks. I have a short video but am unable to attach it. Any thoughts would be appreciated.

Thanks,
Pat

 

[G72Zed]

Please elaborate and give details on the following:

- Accelerator pump at .015"

 

[Pat70Z]

As I understand it I should be able to insert a .015 feeler gage between the pump arm and the linkage when the throttle is wide open. The pump arm should be able to move that .015 without bottoming out. If I am incorrect let me know.

 

[G72Zed]

As I understand it I should be able to insert a .015 feeler gage between the pump arm and the linkage when the throttle is wide open. The pump arm should be able to move that .015 without bottoming out. If I am incorrect let me know.

That train of thought comes from the same place as picking a Power Valve based on the idle vacuum and dividing in 1/2 and adding .5, some things die hard.

I take out the feeler gauge to check/set/adjust lash.....but it's on the rocker arms, not the Holley carb's acc. pump arm, if you are doing that, you are leaving pump fuel volume on the table.

Look at it like this, the diagram, weather it's black/blue/green has a range of almost .300, the pump spring goes into bind about .220-280 pending wire size, cams lift is under that, even with the body arms motion ratio of 1.2, it's not close, spring stack up happens first, that why there's a spring on the arm.

When I get these type of "issues" showing up, I look at, and map out the engines actual timing curve and ignition system, then update or make the required changes, then focus on the carb circuitry and adjustments.

What are the details on the ignition ? what type of fuel is being used, Ethanol content % ?...original intake and gasket, or is their a spacer being used, headers?

With the curb idle screw set at full hot idle, adjust the pump arm to 0 lash, then give it 1/2 turn preload (CCW), and not the reaction time of the shooter.