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Old 07-26-2010, 10:51 AM
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Air getting in accelerator pump?

This problem has been anyoing me for a while. Holley 4160, 80508 750cfm vacuum secondaries.

It is intermittent. If i crank the car up, I usually have air in the acc pump. I pump the gas a few times and then it's clear and works fine. Same happens if I'm cruisng for a while and then pull over, if I pump the gas, it stumbles, but once the air is out, it works great from there on. It's like air slowly gets in it when it's not in use.

I've already changed the acc pump gasket and umbrella valve. Not sure what it could be now.

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Old 07-26-2010, 11:35 AM
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Quote:
Originally Posted by kyle86
This problem has been anyoing me for a while. Holley 4160, 80508 750cfm vacuum secondaries.

It is intermittent. If i crank the car up, I usually have air in the acc pump. I pump the gas a few times and then it's clear and works fine. Same happens if I'm cruisng for a while and then pull over, if I pump the gas, it stumbles, but once the air is out, it works great from there on. It's like air slowly gets in it when it's not in use.

I've already changed the acc pump gasket and umbrella valve. Not sure what it could be now.
Check the flatness of the castings of the main body and the metering block in particular. These often warp, when rebuilding with fresh gaskets, early on things appear normal, but as the gaskets flexibility ages away then tiny air and or fuel leaks develop.

Bogie
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Old 07-26-2010, 11:38 AM
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pin hole in diaphram !
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Old 07-26-2010, 11:41 AM
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Quote:
Originally Posted by oldbogie
Check the flatness of the castings of the main body and the metering block in particular. These often warp, when rebuilding with fresh gaskets, early on things appear normal, but as the gaskets flexibility ages away then tiny air and or fuel leaks develop.

Bogie
Hadn't thought of that. That sounds like what might be happening. Is there a way to fix this if that is the problem? What about doubling up on gaskets?
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Old 07-26-2010, 12:22 PM
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If you remove the squirt nozzle you should find a needle valve in the passage way down the hole. Some have a BB size ball on top of it. Both come out with a magnet. Make sure they are in there. What they do is let the fuel in the passage flow one direction (out the squirt nozzle) when you step on the gas. without them the fuel will bleed back down the passage creating an air pocket in the passage. If they are in there, check the condition of the needle and make sure it's clean and not pitted on the pointed end. A slight easy pump with the needle out will push any dirt or foreign mater out of the passage way.
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Old 07-26-2010, 12:29 PM
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Ye Olde farmer fix...If you have a good quality tablesaw, tape a piece of emory paper or the appropriate grit sandpaper to the table (tape all 4 corners down, dont roll the tape over on itself). The good quality tables used to be checked for flatness...so this will help you remove the requisite material, and you can use a feeler gauge to see where you need to remove material. Also, make sure you move the object in more than 1 direction...either in circles or an X-pattern.

No tablesaw table? use a piece of window glass
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Old 07-26-2010, 12:42 PM
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Quote:
Originally Posted by sqzbox
If you remove the squirt nozzle you should find a needle valve in the passage way down the hole. Some have a BB size ball on top of it. Both come out with a magnet. Make sure they are in there. What they do is let the fuel in the passage flow one direction (out the squirt nozzle) when you step on the gas. without them the fuel will bleed back down the passage creating an air pocket in the passage. If they are in there, check the condition of the needle and make sure it's clean and not pitted on the pointed end. A slight easy pump with the needle out will push any dirt or foreign mater out of the passage way.
x2 Most likely cause
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Old 07-26-2010, 12:50 PM
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Quote:
Originally Posted by kyle86
This problem has been anyoing me for a while. Holley 4160, 80508 750cfm vacuum secondaries.

It is intermittent. If i crank the car up, I usually have air in the acc pump. I pump the gas a few times and then it's clear and works fine. Same happens if I'm cruisng for a while and then pull over, if I pump the gas, it stumbles, but once the air is out, it works great from there on. It's like air slowly gets in it when it's not in use.

I've already changed the acc pump gasket and umbrella valve. Not sure what it could be now.
The check valve seat under the squirter has to be in good condition. If you have a used check of the same type your carb uses, you can use it to carefully reform the seat itself.

You place the check down into the hole, then using a long, thin, flat-ended punch, gently tap the check w/a small hammer. This will remove any raised edges or whatnot that may be causing the check to not seat tightly.

For the bottom check, if you have the rubber umbrella, be sure that it is still very pliable and the sealing surfaces on the carb as well as the umbrella are smooth and defect-free.

If it has the older "ball and bail" style check, use the same procedure as for the under nozzle check to reseat the ball.

Removing and replacing the bail is no fun, and must be done very carefully so as to maintain the slight bend in the bail. It's best to re-peen the metal to secure it back into place. Only do this if it's necessary.

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Old 07-26-2010, 02:30 PM
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I see. I know that my carb has the check needle under the acc pump squirter. I was thinking that it may not be sealing properly causing the fuel to bleed back down like sqzbox and cobalt are talking about. I have a punch that will work. I might give this a try first before pulling the metering block.

So the purpose of this needle is to prevent fuel from seeping back down into the pump diaphram? Since this only happens after the car has been sitting for a little bit or been crusing for a while, this sounds like a very likely cause. Thanks!
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Old 08-18-2010, 04:26 PM
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Update. I taped it with a punch but accidentally hit it too hard and too many times haha. The needle got a little galled up but I put it in and poured in some gas and it seems like it seals up. I drove the car and I think this fixed it!. Thanks everyone!
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