I have a question for the carb guru's as well as anyone who's done the acc pump mod. How many "extra" gaskets do you use? I cannot find a consistent number anywhere, just "a couple in front or back" or "enough to make extra volume" or something along those lines. I have two extra acc pump diaphragms, that I've already cut to use, just wondering if this would be enough? I figured putting them on the spring side of the diaphragm would be best, but again, the answers I am finding are inconsistent. Some images I see, seems like there is almost 5/16" in gasket material stacked up to do this mod! I'm just wondering if there is a minimum to make this work or does adding even 1 extra gasket make a difference?

Every thread I've found and read so far, I've saved to my bookmarks because there is a plethora of other info! This forum and everyone who contributes really is a great help. One of the best forums I've joined....so thank you!

 

I made 4 gaskets out of thick gasket paper. Looks like I used 2 on each side, but I probably should have put them all on the carb side. (When I try to remember I get the nikki and Holley pumps confused). I might have been moving them and adjusting the pump shot. Not sure, I sold the carb a while back, but it definitely increased the amount and duration of the shot.

 

Stupid question, but what does this do to performance? I never heard of this, but my carb is bone stock. I'm always interested in learning!

 

It is to increase the volume of the Acc Pump shot, and the extended lever is to lengthen the duration of that pump shot. So instead of the normal volume of gas that is sprayed in for the transition to more throttle..... you can get more and/or spread it out longer.

Pretty much all carbs have an accelerator pump (nikki, Holley, Webber, Rochester, whatever). When you give it gas the acc pump sprays extra gas to transition between the idle jets and main jets. Without it the motor would lean-out momentarily before the main jets caught up. It helps that transition.

The famous Holley "Double Pumper" carbs have two acc pumps... one for Primary and one on the secondaries. Most 4 barrels just have it on the primaries. On a typical Holley you can change the plastic "cam", which adjusts amount and delivery of the shot. On an Edelbrock you can change the position of the rod and get (almost) the same effect. But there's no provision for adjustment on the nikki, so if you think you need adjustment you do something like this.

 

I'm gonna run 3 on the carb side of the diaphragm. I think this would be a good starting point. Just have to pay attention to the duration and ferocity of the squirt. I'm following jeff20b's instructions for the longer lever. I believe he said the holes are 1-1/4"? with oval holes? I'm just unsure of how much bend to give it, or what the bend accomplishes....

 

The bend is so you can have that much extra lever and the rod still reach it. If the extension was that length and straight the end of the rod doesn't reach it. The hole where the rod attaches/passes through needs to be ovalled a little (length-wise) so the rod doesn't bind, because the angle changes as the pump is stroked. I believe the factory hole is ovalled (for the same reason).

 

Thank you, that explanation is very helpful!

 

Figure I'd just chime in quick about the gaskets. When I did mine I used only one gasket (thick grey paper, I can check the actual thickness later) on each side of the stock diaphragm. I did this for one reason really - I noticed that the diaphragm can't move much further than the additional thickness of one gasket anyway.
​
Essentially I got it to where the diaphragm was almost maxed out in both directions and called that good. My theory here is that I didn't want the diaphragm supporting itself when in it's rest or fully depressed position. To me this is just for slightly improving the life of the diaphragm, but in reality it's probably unnecessary to worry about. In my situation I can say that one gasket per side left a hair of travel/volume on the table, and adding one more gasket per side meant that the diaphragm would not longer contact either side of the AP "housing". Beyond that no travel was being gained.

 

Looks like I'm too late to edit my post so...

Just measured the gasket paper I used and it looks to be 1/32".