It's always something

[patrickt]

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.