AVS bog, accelerator pump adjustment
#3112259
01/15/23 09:13 PM
01/15/23 09:13 PM
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Joined: Mar 2005
Posts: 1,546 Seattle, WA
375inStroke
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Seattle, WA
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I rebuilt a '69 Roadrunner carb, and the accelerator pump doesn't squire till the secondaries start opening. The spring on the pump compresses without the piston moving at first until it can overcome the spring under the pump, and the resistance of the fuel. There was no check valve in the carb. I took one from another AVS that had been messed with. The pump works the way the FSM says to test it, but there is no fuel squirting while only operating the primary throttle. The secondaries are adjusted per FSM, two complete turns after the air door just starts to close. The thing just doesn't have crisp throttle response, and that's just in neutral. Timing is 38deg. total with vacuum disconnected. It idles with the throttle turned one and a half to two turns from fully closed, and there's vacuum on the ported vacuum port. I'm wondering what to do next.
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Re: AVS bog, accelerator pump adjustment
[Re: 375inStroke]
#3112334
01/15/23 11:56 PM
01/15/23 11:56 PM
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Joined: Aug 2003
Posts: 43,308 Bend,OR USA
Cab_Burge
I Win
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I Win
Joined: Aug 2003
Posts: 43,308
Bend,OR USA
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What size and weight check valve did you use? It should start to squirt when the pump skirt is at the top of the fuel inlet slot, I check them that way without the tops first to make sure the pumps work
Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
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Re: AVS bog, accelerator pump adjustment
[Re: 375inStroke]
#3112382
01/16/23 03:23 AM
01/16/23 03:23 AM
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Joined: Aug 2003
Posts: 43,308 Bend,OR USA
Cab_Burge
I Win
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I Win
Joined: Aug 2003
Posts: 43,308
Bend,OR USA
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there are several different version of the check valve that will go into those holes, both triangle and square versions. Can you take a picture of yours and post it on here? You might want to check the seat in the carb where the check valve seats to make sure it isn't corroded a bunch, if it is corroded that will allow the gas to be suck out of the well when driving it making it not pump also. How about the check valve at the bottom of the accelerator well, is it sealing when being pumped or allowing the gas to be push back into the carb body?
Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
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Re: AVS bog, accelerator pump adjustment
[Re: jwb123]
#3112422
01/16/23 10:37 AM
01/16/23 10:37 AM
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Joined: Mar 2005
Posts: 1,546 Seattle, WA
375inStroke
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I see the spring I'm talking about is called a delay spring. Well, that's what it's doing. The bottom of the squirter port is clean and shiny. The needle moves freely. I'll try and stretch the delay spring out a bit. I've read some people make the needle shorter/lighter, and some people say to never do that. The 4618 eBay carb I rebuilt years ago worked fine, and still does. No delay in the pump. I can't remember what kind of check valve it had, though.
Last edited by 375inStroke; 01/16/23 10:40 AM.
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Re: AVS bog, accelerator pump adjustment
[Re: lewtot184]
#3112430
01/16/23 10:57 AM
01/16/23 10:57 AM
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Joined: Jun 2014
Posts: 1,340 VA
dragon slayer
pro stock
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pro stock
Joined: Jun 2014
Posts: 1,340
VA
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The delay spring should not be a heavy spring. Originals are thin dia coil wide spacing. The spring on the pump is heavier. There were different diameter pumps, and the cylinder can be worn. But since you say your collapsing the pump rod, that eliminates undersized pump and even missing check valve, all which would reduce pressure against the pump going down. So it seems to me the pump spring and delay spring are swapped or wrong.
The check valve under the carter pump housing are brass with point. They can get stuck, but if it does shoot at some point something is off. I have seen folks add ball bearing on top of it for some reason. As long as not rigged somehow it seems to me the springs are the issue.
One last thing, no free play in the lever on throttle shaft going to the pump rod causing it to delay movement?
Last edited by dragon slayer; 01/16/23 10:58 AM.
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Re: AVS bog, accelerator pump adjustment
[Re: dragon slayer]
#3112470
01/16/23 12:02 PM
01/16/23 12:02 PM
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Joined: Mar 2003
Posts: 9,102 Rogue River, OR
Jeremiah
master
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Posts: 9,102
Rogue River, OR
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I have had AFB and AVS carbs with the same trouble. As mentioned you might try an edelbrock accelerator pump or call one of the carb specialists like Harms. In my experience the accelerator pumps supplied in the Hygrade kits usually don't work correctly. The accelerator pump should spit fuel as soon as the on the throttle linkage moves.
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Re: AVS bog, accelerator pump adjustment
[Re: Jeremiah]
#3112743
01/16/23 11:05 PM
01/16/23 11:05 PM
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Joined: Mar 2005
Posts: 1,546 Seattle, WA
375inStroke
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I took the needle and return spring out, and it acts the same. It's like the leather seal is creating more friction than the delay spring rate. I stretched the delay spring out a bit, put the needle and return spring back, and I think it's even worse. Looking at the pic blown up, the new seal's starting to look worse than the old one. Guess I've been messing with it too much. Guess I'll try one of those viton, or whatever rubber type seal. Needle, return spring, nozzle, old, and new pump Down the discharge nozzle channel.
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Re: AVS bog, accelerator pump adjustment
[Re: Jeremiah]
#3112747
01/16/23 11:08 PM
01/16/23 11:08 PM
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Joined: Mar 2005
Posts: 1,546 Seattle, WA
375inStroke
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In my experience the accelerator pumps supplied in the Hygrade kits usually don't work correctly. Ok, Standard Motor Products is Hygrade, right? Lol, that's what I've been using. They used to be top of the line when I was taking auto shop in school.
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Re: AVS bog, accelerator pump adjustment
[Re: lewtot184]
#3112925
01/17/23 05:01 PM
01/17/23 05:01 PM
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Joined: Mar 2005
Posts: 1,546 Seattle, WA
375inStroke
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The inlet check valve is fine. If I plug the outlet, and push down on the plunger, both slowly, and forcefully, and no fuel backs out of the inlet check valve either time. With the outlet check needle and squirter removed, I can push down on the rod, the spring compresses without the plunger moving, then when the rod is completely collapsed, the plunger moves down, pumping gas out the discharger freely, lots of flow. Did this without the return spring installed, too, so all I can think is the leather seal has too much friction. I'll try the Edelbrock 1470 pump tonight and see what happens.
Last edited by 375inStroke; 01/17/23 05:02 PM.
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