Holley DP Accelerator Pump

Bandana,
Let's break this up.
"- Adjust the spring compression so that at WOT you can slip a 0.015" feeler gauge between the pump plunger rod and the spring loaded rod with "some resistance". When the gauge is pulled out the plunger rod should move up the 0.015" it was depressed."
"So, does this sound about right? If so I find it full of ambiguity... I will start by saying that my plunger was real tight. The linkage rod was pushing down on the pump plunger so hard I couldn't begin to get a gauge in it until I tightened the spring up a good 1/4". Right now I have it set so I can poke the 0.015" gauge between the two arms. What I find ambiguous with this setting is just how tight the gauge should be??"

Check this first. You should aim more at @ .020". The idea here is you don't want to bottom the pump out into the float bowl because it will cause the pump diaphragm to fail prematurely. When you adjusted it, make sure the spring isn't experiencing coil bind. Check it at WOT and with your finger press the pump until it bottoms out and the feeler gauge should fit in easily. If there is more clearance this is not a problem other than it could limit the pump shot some.

"- make sure that the spring loaded arm just touches the pump plunger rod at idle with no slack. (I'll come back to this one)..."
"Going back to the first adjustment - my pump plunger rod as a bit of play in it. If I adjust it so that there is barely contact then there is a tiny bit of slack before you can feel the plunger rod meet the diaphragm inside. Is this bit of slack normal ? Am I right to adjust the slack out so there is a direct movement between the throttle and the plunger?"

This is really the second adjustment. The slack needs to be removed. The idea here is if you even breathe on the throttle you want the pump to begin to shoot fuel. You can either open the spring back up by loosening the adjustment or move the initial position on the accelerator pump cam. There is a small flat screw that holds the cam on at the base of the throttle shaft. They usually have two or three numbered holes in them. This allows you to change the timing/duration of the pump shot. Try changing to another hole and re-check to ensure you still have the .020" clearance at WOT. Adjust if necessary, then re-check to see if you are engaging the pump when you move the throttle. They make several different cams and you can recognize them by color. If you have access to some you can try changing them out until you get it where you need it. If you need some I have piles of them and I could drop an assortment in the mail to you. Any change you make just be sure and double check the first adjustment or you will end replacing the diaphragm. Hope this helps. Maybe I should make a video.
spiritdude

If you want instant off-idle response with no bog, need pretty much no gap at idle, but it will hurt fuel consumption a bit when you're just easing into the throttle during normal driving and may not have enough shot to cover full throttle.

Edited by Red Devil - Jul/28/2017 at 8:39pm

Thanks guys for feedback and help. My accelerator pump was set too tight - very close to bottoming out if not so....After working on it I have the play at idle just taken up and have a good tight fit of the 0.015" feeler gauge at WOT. This seemed to help some. Watching yet another You Tube video while on a beer break about the cams I checked and mine was set in the #1 hole for low idle engines. Mine idles around 900rpm. Put it in the number two hole and it made a significant improvement. I can almost mash the throttle without a burp. I think I need to get a cam kit and maybe some squirters to take it from here.. Tomorrow I'll take her for a drive and see what I have in real life....

If the engine stumbles immediately upon hitting the throttle, you need to up the squirter for a bigger initial shot. If it starts out fine and then stumbles, the squirter is adequate but the pump shot is running out too soon. Then you need to put in a bigger cam.

The total lift of the pump cam is what determines the amount of fuel dispensed in one stroke of the pump. Holley has charts that show the lift of the cam on their website. The cam profile does not make a difference if you mash the throttle, just the overall lift. Once you have that worked out, you can play with the profile to fine tune the part throttle response to exactly your combination and driving style, if needed.

So, here is the order of ops to set the accelerator pumps up:

1) squirter size. Increase it until you get a good instant response.
2)cam lift, IF the shot of fuel runs out too quick.
3)cam profile, to fine tune the part throttle drivability.

As for setting the preload on the pump arm, one suggestion that works for me is to turn it until it just touches and then turn it one or two more flats on the adjusting nut to give it a bit of preload.

I hope that helps!

Chris

The second hole is so that if your engine has a lumpy cam and requires a high idle, you are not already taking up some of the pump travel just by opening the throttle plates enough to idle. Basically it retards the pump cam about 15 degrees, if memory serves.

Chris