Accelarator pump cam question

• Dec 7, 2019

• #1

JG1966

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I'm having some carb issues on my 340 with an AED Holley 750 DP. Not sure if I found a problem. Is the arm on the primary accelerator pump supposed to sit directly on the cam? I have a gap and the cam doesn't actuate the pump until nearly full throttle. Secondary arm sits right on cam and squirts immediately. When I press accelerator pump independent of the arm, I get gas immediately but the arm is loose and I can lift it about an 1/8th inch. Is this right? Thanks

 

• Dec 7, 2019

• #2

Lefty71

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https://www.google.com/search?sourc...DCAc&uact=5#kpvalbx=_wvnrXe2FHsq0swXkrIzwCQ22

Sounds to me like your pump diaphram might have become brittle and is not returning correctly.

 

• Dec 7, 2019

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Badvert65

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You can adjust the clearance on the cam with the bolt that rests on the pump lever. You basically want zero clearance. Any gap and you get a delayed pump shot and this is very noticeable in the throttle response.

 

• Dec 7, 2019

• #4

JG1966

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Badvert65 said:

You can adjust the clearance on the cam with the bolt that rests on the pump lever. You basically want zero clearance. Any gap and you get a delayed pump shot and this is very noticeable in the throttle response.

Click to expand...

Thanks Badvert. That's what I figured. I think I found my issue. Just not sure how it got so wildly out of adjustment.

 

• Dec 7, 2019

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Lefty71

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JG1966 said:

Just not sure how it got so wildly out of adjustment.

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This is what Im saying as well... unless the nylock nut is shot, the only reason it should change is the diaphram is getting crappy, and adjustment will be temporary, if it helps at all. My experience with bad diaphrams is they are tough, but once they are'nt supple any more, it's time to go.

 

• Dec 7, 2019

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JG1966

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Lefty71 said:

This is what Im saying as well... unless the nylock nut is shot, the only reason it should change is the diaphram is getting crappy, and adjustment will be temporary, if it helps at all. My experience with bad diaphrams is they are tough, but once they are'nt supple any more, it's time to go.

Click to expand...

Thanks Lefty. The nylock nut is fine. I'm pretty sure it's a diaphragm issue. Time for a change.

 

• Dec 7, 2019

• #7

oldbee

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A Holley diaphragm is set for .015” clearance at full throttle with pump lever bottomed out. That’s so with it on car you don’t bottom out pump lever at full throttle.