Activation of the accelerator pump causes fuel to come out of the squirter, not the boosters.



Yep!

Quote:

Originally Posted by FWB (Post 1427162) and a note for "experts"

Yep again. You want immediate movement of the accelerator arm with any throttle movement. You DON'T want coil bind (bottoming or stacking the coil spring) at WOT. THIS will over pressure the diaphragm, causing a tear.

The spring stays in a relaxed state from idle to near WOT.
As the throttle/accelerator pump arm nears WOT you want to run out of throttle motion first, before you reach the end of travel for the pump arm. There should be 0.015 inch travel of the pump arm remaining once you hit WOT with the throttle. If you hit the max travel of the pump arm first, further travel of the throttle will start to compress the spring. Once the spring compresses completely, this is called stacking or coil bind - it cannot compress anymore. After this point, the weakest spot in the system is the pump diaphragm and it will tear as it gets over extended.

Let me help you understand this better...
 

Let me clear this up for you, as it is a very common misconception in the carburetor-powered community.

The Holley accelerator pump adjustment instructions, that have not changed in 50 years, suffer from two shortcomings: 1) They were poorly worded even back when I was a wannabe-hoon in the 1970's; 2) The instructions are "catch all" instructions for every cam available for every installation on every carb.

That said, you should understand the intent behind Holley's description of the need for a .015" gap. That verbiage is included in the instructions to alert the installer that if the actuator is pushed really, really far in to the pump canister then you could possibly tear the diaphragm. That's why the gap is specified at WOT, with the actuator pushed as far as it will go in to the canister, NOT at idle (where it's pushed in not at all, or maybe just a hair). In other words, Holley is saying "when you're pushing the throttle as far as it will go, you should still have a little more room to go on the actuator so that you don't tear the diaphragm." That's it. That's all it means.

Now, by far, the most common malady with accelerator pump adjustments is that the installer leaves a gap between the cam and lever at idle. This causes off-idle problems and overall poor performance. You want NO gap between the cam and lever at idle and, the best way to do this, is to have a slight preload.

So why can I safely IGNORE Holley's instructions on the need for a .015" gap at WOT and just adjust my accelerator pump to have a slight bit of preload at idle? Because if you look at the pump cam lift dimensions of the different cams that Holley sells you will see that the larger cams have way more lift than the cam you are likely using. Much more than that .015" gap you're looking to keep at WOT. That means that it is virtually impossible to bottom out and tear your diaphragm, from casual mis-adjustment, with anything other than the largest colored cams that Holley sells. In other words, unless you are running one of the very biggest cams Holley sells, then you don't even have to think about the .015" thing.

I hope this helps to put your mind to rest.:cool:

Yeah, that's what I said.

But FWB needs to hear things more than once before it sinks in.:rolleyes:

The accelerator pump circuit discharges from the accelerator pump nozzle, not the booster venturis.

Accelerator pump nozzle is secured with one screw between one pair of venturis.

The booster venturi is centered in each venturi, where main circuit emulsion discharges from.