Acellerator pump repleshiment

[genolan]

I have a question about the holly 30cc accelerator pump. When is the pump replenished with fuel. If you hit the accelerator hard does it need to return to idle position to refill or is it always being refilled when you reduce throttle?

[Jerry Clayton]

there is an internal spring that pushes the diaphragm back down when the throttle is relaxed drawing fuel back into the chamber past a rubber check valve----------

[DesertMK4]

The Holley pump works off a cam on the driver side of the carb. This cam pushes down on a lever. The lever then pushes the diaphragm on the pump. The pump then sends an extra gas squirt into the throttle bore. This is intended to smooth the transition as throttle is opened by enriching the mix. The pump only works when the throttle is opened more. A spring on the diaphragm returns it and draws more gas into the pump. You get no pump action at a steady state of throttle. Holley has videos on adjusting the pump, lever, cam and squirt nozzles.

[genolan]

I was also wondering if the 30cc pump would deliver fuel along the entire travel of the cams outlined in the Pump Cam Lift VS throttle position graph on the holly site. I realize that a .25 squirter would last longer than a .35. So at what throttle rotation(in Degrees) would a .35 squirter on a 30cc pump run dry?

[Gaz64]

Originally Posted by genolan

I was also wondering if the 30cc pump would deliver fuel along the entire travel of the cams outlined in the Pump Cam Lift VS throttle position graph on the holly site. I realize that a .25 squirter would last longer than a .35. So at what throttle rotation(in Degrees) would a .35 squirter on a 30cc pump run dry?

On gentle throttle opening rates, the nozzle stops flowing when the cam lift versus duration stops, re: cam durations.

The throttle could be slammed open and the nozzle still flows fuel. The purpose of the override spring. Nozzle duration is shortened with larger nozzles.

A "25" squirter is .025 inch, not .25 etc.

[Rick Parker]

There is also a spring on the accelerator pump actuating lever that compresses to prevent damage to the pump diaphram when the throttle is slamed open. it is designed to prevent damage to the diaphram which could possibly burst otherwise. The spring also to some extent controls the flow rate as "IT" limits the force that actually pushes the fuel. At idle there must be a small clearance (.015??) between the pump arm and the lever.
On another note, it would be well advised to seek out the diaphrams intended for alchohol fuel marketed by various companies and use them to replace the standard Black rubber Holly diaphram. Most areas have varying degrees of Alchohol in their gasoline and it will attack the traditional rubber diaphram.

[Gaz64]

Rick,

The .015 is a check at wide open throttle, an old holley theory.

Who checks for that these days?

Adjust the pump for clearance at idle, AND THEN take the clearance out.

After any pump cam change.

[Rick Parker]

Gary: You are correct. Brainfart on my part