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4401s accelerator pump "Intake Check Ball" leak #1792575
03/31/15 01:16 PM
03/31/15 01:16 PM
Joined: Sep 2010
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Indiana
pugdog1 Offline OP
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pugdog1  Offline OP
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Good morning:

Rebuilt a 4401s AVS for a 1968 Roadrunner. (Thanks to everyone for help with the idle setting question in the other post.) Reinstalled carb and have a bad backfire through the carburetor when really stepping on the pedal. The accelerator pump shot seems inconsistent. Sometimes it works and sometimes it does not.

During the rebuild I filled the bowl with fuel, installed the plunger, and gave it a push. I was able to get a consistent, strong pump shot.

One thing I noticed that did not "click" at the time was that fuel was also shooting out of the "intake check ball" back into the fuel bowl. But since I had a great pump shot, I just went ahead, finished the rebuild, and reinstalled the carburetor. Given the backfire I think I need to revisit the issue.

So... Should fuel be shooting back out of the "intake check ball" the the plunger is pressed?

If this is a sign of a defect, are replacements available?

Thanks again

Dan

Re: 4401s accelerator pump "Intake Check Ball" leak [Re: pugdog1] #1792576
04/01/15 12:09 PM
04/01/15 12:09 PM
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Lincoln Nebraska
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RapidRobert Offline
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Are you thinking the pump shot is inconsistant cuz of the occaisional backfire or cuz some of the shot went backwards everytime you pushed it during assembly? Yes the ball should be sealing it but I'm wondering if there is something else going on but for starters you might pull the throttle 10 times & see if you get 10 good shots & if they're healthy enough maybe the backflow is inconsequential and I'd put 2 pieces of clean rags in the venturis to catch the fuel as you dont want to wash down the rings. For the backflow You could pull the top & the plunger & ball & blast the hole that the ball sets in & check the ball for imperfections if you are not getting a healthy/adequate shot every time. All OE AVS's are lean but I'm thinking something (vac leak) other than the AP. Yes a common ball bearing of the right size will work. holler back.


live every 24 hour block of time like it's your last day on earth
Re: 4401s accelerator pump "Intake Check Ball" leak [Re: RapidRobert] #1792577
04/01/15 12:41 PM
04/01/15 12:41 PM
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lewtot184 Offline
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those check valves always had some issues. the edelbrock carbs don't use them. you can try taking it out and cleaning it real good and perhaps "staking" the ball to re-seat it. worst case scenario just stake a piece of lead shot in it to block it off. spitting thru the carb is a sign of a lean condition or late timing. i always down size squirters for drivers. this can be done with the edelbrock squirters and a slight modification. the leather accelerator pumps are trouble some. the plastic/viton pumps work much better.

Re: 4401s accelerator pump "Intake Check Ball" leak [Re: RapidRobert] #1792578
04/01/15 01:16 PM
04/01/15 01:16 PM
Joined: Sep 2010
Posts: 17
Indiana
pugdog1 Offline OP
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Indiana
Quote:

Are you thinking the pump shot is inconsistant cuz of the occaisional backfire or cuz some of the shot went backwards everytime you pushed it during assembly? Yes the ball should be sealing it but I'm wondering if there is something else going on but for starters you might pull the throttle 10 times & see if you get 10 good shots & if they're healthy enough maybe the backflow is inconsequential and I'd put 2 pieces of clean rags in the venturis to catch the fuel as you dont want to wash down the rings. For the backflow You could pull the top & the plunger & ball & blast the hole that the ball sets in & check the ball for imperfections if you are not getting a healthy/adequate shot every time. All OE AVS's are lean but I'm thinking something (vac leak) other than the AP. Yes a common ball bearing of the right size will work. holler back.




Thanks Robert:

1) I watched the pump shot after we got the backfire. It would just spit and spurt out. Definitely did not look right. Car ran great for a few minutes after rebuild until it got warm then backfired. (Don't know if this is just a coincidence though.)

2) I am assuming the pump shot was adequate on occasion because sometimes the backfire happened, sometimes it did not. I am assuming that the times it did not backfire the pump shot was good. Maybe not a good assumption???

3) Would not backfire when applying the throttle in park or neutral. Only under load.

4)I did pull the "intake check ball" out and cleaned it during the rebuild. (This is the thing that looks like a jet at the base of the accelerator pump well and unscrews like a jet. I am referring to it by its proper, somewhat misleading FSM name, as it is definitely not just a ball.)

Dan

Re: 4401s accelerator pump "Intake Check Ball" leak [Re: pugdog1] #1792579
04/01/15 01:26 PM
04/01/15 01:26 PM
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Lincoln Nebraska
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RapidRobert Offline
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Alright, maybe we need to locate another one of those check ball assys to start narrowing this down. Tho I am thinking that it there was no vac leak that a warmed up eng would only have a flat spot/hesitation if the AP was non op/inadequate (part or full time) & not be coughing back thru the carb but I ain't 100% sure on that. EDIT one of my fav tricks for this is to block the rods up & take her out for a cruise & see what being on the power circuit does to its behaviour

Last edited by RapidRobert; 04/01/15 01:35 PM.

live every 24 hour block of time like it's your last day on earth
Re: 4401s accelerator pump "Intake Check Ball" leak [Re: lewtot184] #1792580
04/01/15 05:50 PM
04/01/15 05:50 PM
Joined: Sep 2010
Posts: 17
Indiana
pugdog1 Offline OP
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Indiana
Quote:

those check valves always had some issues. the edelbrock carbs don't use them. you can try taking it out and cleaning it real good and perhaps "staking" the ball to re-seat it. worst case scenario just stake a piece of lead shot in it to block it off. spitting thru the carb is a sign of a lean condition or late timing. i always down size squirters for drivers. this can be done with the edelbrock squirters and a slight modification. the leather accelerator pumps are trouble some. the plastic/viton pumps work much better.




Thank you Lew

What do the Edelbrock carbs use in place of the intake check ball? Do they just plug the hole?

You are on to something I think. That assembly may be bleeding off a necessary portion of the pump shot causing a lean backfire.

Base timing is 10 degrees BTDC with the vacuum advance disconnected. I not get a chance to see if it was advancing properly.

I did some research that lead me using the leather plunger. I am wondering if that was not a good choice too. Will put a Viton plunger on the list of things to try.


Thanks again

Dan

Re: 4401s accelerator pump "Intake Check Ball" leak [Re: pugdog1] #1792581
04/01/15 08:51 PM
04/01/15 08:51 PM
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lewtot184 Offline
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lewtot184  Offline
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the edelbrocks are not machined and don't even have the boss for the check valve. the old leather pumps don't create a positive seal in the pump well. there's probably several issues here that need to be addressed, not just the check valve. i imagine those check valves have been obsolete for decades. there's even a similar check valve at the bottom of the pump plunger. when i re-did my 4618s i got rid of the old stuff i knew was problematic back in day. my 4618 drives beautiful.







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