Hemi AFB accelerator pump issue - initial bog on opening throttle

[Geoff 2]

AR67,
Are you sure from the gasket surface to the bottom of slot is under 1"? Looks much longer.
The one way valve is 5/16" diam. Three of those side by side is nearly an inch; the relativity of it in the pic makes the slot look much longer than three jets stacked on top of each other.
I measured 3 carbs: one AFB & one 750 AVS, both 1.050". The other AFB was exactly 1".

 

[AR67GTX]

I did a bunch of measuring and with the 2.82” long AP the leather seal is just seated in the top of the pump well with a top of rod setting of .54”. And that is just shy of 1/4” below the slot. So, I’m going to shoot for a top of rod setting of 11/32 to 3/8” and do what I can to get it pumping strong.

Some more rambling thoughts. Still unsure how immediately I should see fuel from the squirter when moving the throttle on an AFB. Never had to dig this far into this subject on an AFB or Edelbrock before. From some of the videos on Mikes Carburetors website, it takes a fast and nearly full travel of the throttle to get fuel out of them - a slow or moderately fast operation won’t do it.

I‘m not sure of why the slot on a Carter AFB anyway? On my 800 Edelbrock it actually feeds the accelerator pump and the pump height has to be carefully adjusted to barely expose the slot with throttle closed to recharge the pump. But this series of Carters use a feed port with check at the bottom of the well so not sure what the slot does other than maybe keep the top of the seal wet, and prevent gas from building up on top of the pump. But it wouldn’t need to be so deep of a slot to do any of that.

 

[AR67GTX]

AR67,
Are you sure from the gasket surface to the bottom of slot is under 1"? Looks much longer.
The one way valve is 5/16" diam. Three of those side by side is nearly an inch; the relativity of it in the pic makes the slot look much longer than three jets stacked on top of each other.
I measured 3 carbs: one AFB & one 750 AVS, both 1.050". The other AFB was exactly 1".

I went out and double checked and did make a mistake using the bottom of my caliper somehow. I may have set the tip on that flashing in the bottom or set the bottom crossbar of the slide instead of the slide bottom on the top. I remeasured it at 1.053” this time and the constant dia well measurement was still measuring at 1.22” or .170” further down? Bottom seat in well depth is 1.86”.

Since my top of rod setting is based on the top of the compression portion of the well, plus a random .2” addition seating, it is unchanged.

Sorry for the bad measurement.

 

[mrhemi]

Shinning light on the gas surface I think I could detect a bit of backflow. I removed it, cleaned it and blew it out and re-tightened it. Didn’t seem to be doing it anymore but I went ahead and ordered two replacements. Also double checked the squirter gasket and check weight and OK. BUT - can’t adjust it out. Even straightening the rod nearly out and putting it on the outer hole, I don’t get fuel until about 1/4 to 1/3 throttle like this With the top of rod almost at top of lid.

View attachment 1415365

I ordered from Mikes Carburetors and she confirmed my pump length within a few thousands. Their tech support is by email so I sent them a bunch of pictures, measurements and observations. Maybe I need to fine polish the bore a little or the pump umbrella is defective. It doesn’t seem to be recharging through the bottom jet as well as it should - which could be a sealing issue too. I removed the check valve in this pic. Have to see if they have some ideas.

View attachment 1415366

I squirted some fuel in the fuel bowl of the front carb that’s still on the car to see what it does. Same thing, nothing until at least half throttle and the top of the rod is at least below 1/8 off the lid. So, seems to be universal to the 2 carbs.

The first photo seems to show the pump link installed in the hole in the lever furthest from the fulcrum, although the photo is not the best. On a '69, that link should be in the center hole of the lever. That would give you more pump stroke per throttle movement, which seems to be your problem. Not sure how it was on a '66 setup though, but something to consider.
Also, I have a set of '69 carbs apart that have not been altered. I can measure the depth of that slot in the pump well when I get out in the shop if you want.

 

[AR67GTX]

I’ve experimented with every hole trying to get the rod length and top of pump adjusted to 3/8”. Middle hole is what I’m using though - had to nearly straighten the rod to get the pump height down to 3/8”.

Polished the well. Lightly tapped the checks to make sure they seat well. Put light coat silicon grease on squirter gasket to be safe. Set top of pump at 3/8”. This is the throttle point that I feel resistance in the accelerator pump and it will squirt fuel. It’s at least half throttle. Normal?

 

[AR67GTX]

OK took the top back off and massaged the pump by hand and it sunk in what I’m feeling. The delayer spring is compressing in the first half of throttle travel and the pump is stationary in the well. At about the half throttle pump the pump resistance overcomes the spring and it starts to move and fuel is squirted. Pretty much how I understood it works, but just surprised the spring doesn’t begin to move the piston well before half throttle.

The other observation is that once the pump bottoms the delayer spring and begin’s to move down - the spring never releases and pushes the piston down which I thought was part of its function in order to extend the shot of fuel. But the springs stays compressed until the pump is released and begins to rise back up.

I know there‘s on off-idle transition circuit in the idle system but it’s pretty much all in with the first 10 degrees or so of throttle opening and then nothing more until about 50% throttle when the accelerator pump kicks in.

So does this sound normal or should I suspect the delayer springs might be a little too soft? To me it should be stiffer?

 

[turbine68rt]

OK took the top back off and massaged the pump by hand and it sunk in what I’m feeling. The delayer spring is compressing in the first half of throttle travel and the pump is stationary in the well. At about the half throttle pump the pump resistance overcomes the spring and it starts to move and fuel is squirted. Pretty much how I understood it works, but just surprised the spring doesn’t begin to move the piston well before half throttle.

The other observation is that once the pump bottoms the delayer spring and begin’s to move down - the spring never releases and pushes the piston down which I thought was part of its function in order to extend the shot of fuel. But the springs stays compressed until the pump is released and begins to rise back up.

I know there‘s on off-idle transition circuit in the idle system but it’s pretty much all in with the first 10 degrees or so of throttle opening and then nothing more until about 50% throttle when the accelerator pump kicks in.

So does this sound normal or should I suspect the delayer springs might be a little too soft? To me it should be stiffer?

As stated in post #2 it sounded like you may have the wrong diameter diaphragm for your particular bore and may be binding. Can you measure your bore to verify what diameter AP you need? Even with my 4429 there are 2 possible diameters. Ask me how I know what happens when your bore is made for an 11/16 AP but you get a 3/4.

 

[turbine68rt]

I had Harold restore an AVS for me. Very nice quality work.

 

[AR67GTX]

The closest I could get on the well bore with a snap gage was .732” dia. The pump leather skirt, which was been in use measures .746” which I assume is a 3/4” pump. So I have around . 014“ interference fit.

I suspect the springs on the pump aren’t well balanced but since my main issue is a bog when rolling into the throttle, I’m going to try the standard approach of putting the rod in the inner hole on the rear carb and see if that takes care of it.

 

[Geoff 2]

AR,
There were two AFB/AVS pump bore diameters, 3/4" & 13/16". You have the smaller one which means the plunger has to be correct because the larger simply would not fit! The leather cup ones are best, which you are using.
Note that the Edel carbs use the horrible rubber cup, which enabled them to omit [a] the brass one way inlet valve at the bottom of the chamber & the safety spring.
The two springs: the spring on the pump shaft is the safety spring. If the pump outlet was to become blocked, the spring compresses rather than allow the linkages to bend. This spring is MUCH stronger than the other spring which sits underneath the plunger; the job of the lower spring is to keep take all the slop out of the linkages so that pump shot is as instantaneous as possible. The sloppy fit of the rubber cup used in the Edel carbs [ & TQ ] allows deletion of the safety spring & inlet valve.

I doubt either spring is the cause of any problem. I have seen different length pump plungers for AFBs. I suspect yours is too short & therefore you are not getting the full pump shot.
The holes on the pump arm perform the same function as the pump cams on H carbs.
Going to an inner hole gets the pump shot activated quicker, but it also shortens the duration of the shot.

 

[Geoff 2]

Sorry about the bold, still half asleep...

 

[AR67GTX]

I’ve ordered another pump/spring from Mikes Carburetors but that’s where my others came from too however. I’ll compare them when it gets here. Debating whether to trim a few coils off the lower springs to see what happens. Might try that when the spare gets here. I may have another spring from before too - will check. Might be an Edelbrock spring.

 

[Geoff 2]

Do not trim the spring, it is not the problem. As I explained, it keeps the linkages under tension for instant activation. Softening/removing the spring can cause a delay.

 

[AR67GTX]

Several people have commented that my pump size could be 11/16”. Measuring the widest part of the leather skirt I got .746, figured it as 3/4”. The diameter of the well is about .732” which is a lot larger than 11/16”. So I’m not sure how they dimension these. I’ve ordered a replacement from Mikes Carburetors by carb number so I will wait until it arrives and see if it’s smaller. To add confusion this is what their website shows for 4139/4140 - 11/64”????

Cater AFB 4 Barrel Accelerator Pump 11/16 x 2.29 AP237

 

[AR67GTX]

I had Harold restore an AVS for me. Very nice quality work.

Yep, that’s a pretty good tape. I apparently screwed up measuring the well also yesterday as now I get .73”. He measured .75” well diameter I think for that Pontiac but received 11/16” pumps in the kits from Mikes Carbs. That would also correspond a lot better with my measurement of the pump skirt. Fourteen thousands interference fit didn’t sound right. So a 3/4” pump probably is correct although their website lists a 11/16” pump for 4140/4139 So figure that out??? I’ll be curious to see the one I ordered from them by carb number yesterday, when it arrives.

However I may have stumbled on one issue - the delayer spring and the bottom spring on my pump are indistinguishable. I think they put 2 delayer springs in my rebuild kits. I dug out what I think is one of the bottom springs that was in the carb before the rebuild and it’s much shorter and softer. Old bottom spring is on the left and new spring set (delayer and bottom) are the 2 on the right. The two on the right are identical and I didn’t catch it when putting the carbs together. That probably explains most of my problem. Need to get a couple proper springs.

 

[Geoff 2]

Well this gets interesting.
In the Woodruff chart # 4428 & 4429 [ both AVS Chry carbs ] are listed as having 11/16" pumps. I have both of these carbs & they have 3/4" pump bores. I also measured 6 other carbs I have, one from a 59 Cad; all have 3/4" bores. I have over a dozen pump plungers, all are 3/4". There is some slight differences in the washer diam, but that is because the leather cup with garter spring inside is self centering & the washer OD is not critical.
If you have been supplied a 11/16" plunger by mistake, then the washer OD on the plunger will tell the story. Be careful though....One of my plungers had a 0.700" washer. That is 0.003" too big for a 11/16" bore & would bind. It is for a 0.750" [ 3/4" ] bore, slightly too small for reasons above.
What I also find strange is that repair kits for production AFB carbs came with one plunger, 3/4"& not a 11/16" enclosed as well.

 

[mrhemi]

I'll add to the plunger spring confusion / question.

The plunger on the left is from a '69 Hemi AFB. It is probably an original since it has been in a box with the dis-assembled carb since 1976. The center plunger was in the box as well, but is unused, probably an actual Carter piece. The plunger on the right is from a Standard Motor Products rebuild kit from about 30 years ago. Note the difference in the springs. The original (left) and center plunger have nearly twice the spring pressure as the newer plunger on the right. The cardboard protector sleeves appear different sizes but the actual plungers are all the same diameter.
Approx. two years back I rebuilt the carbs on my '69 and used kits sourced from Carquest, (which were actually Standard Motor Products kits) and experienced none of the issues you are.

 

[mrhemi]

Going to an inner hole gets the pump shot activated quicker, but it also shortens the duration of the shot.

Not quite true, the pump stroke will actually increase. Basic lever mechanics.

 

[Dragon Slayer]

I did not see this thread, but was helping Dan via PM. All the MOPAR early AFBs used 11/16" pumps. 64-212. Even Max wedge used it 64-279. Not until later MOPAR AVS did they shift to larger dia pump. Dan, the spring on your left in your picture is the return spring. Much weaker than the delay spring on the pump shaft. It is not supplied with the kits normally. Center hole of arm at 7/16" is the spec.

The pump circuit is the same on both hemi carbs, and you cannot switch a front and rear since the levers are different, and effect the progressive linkage.

The fact that your compressing the pump delayer spring before the pump is moving has to be the issue. Between a too heavy return spring and the hydraulic pressure of shooting fuel, the pumps isn't moving like it should.

Original pumps with have carter 64-212 stamped, the after market is all over the place with 237, 623, etc...

 

[Geoff 2]

Post #38.
No, very true. I said nothing about pump stroke. By going to an inner hole, the plunger travels further in the same time; this creates more pressure which forces fuel out of the pump nozzle at a faster rate for a shorter duration.