ATM/Holley verses Carter 625 AFB

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The original Carter pieces are quality the FM not so much.
 
Hysteric said:
The original Carter pieces are quality the FM not so much.
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I agree. I’m pretty sure (abut not 100%) it’s not a FM piece.

That carb has been on the shelf for probably 3-4 years since I last used it. So I haven’t had my eyes on it that close.
 
Newbomb Turk said:
It’s not so much that, because I love doing that work. But getting it to fit correctly on these manifolds is the chore.

I don’t want to carve up the manifolds, and I’ve already tested a couple of the adapters and they suck.
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They've always sucked and you cannot tell anyone that. They don't listen.
 
Newbomb Turk said:
I agree. I’m pretty sure (abut not 100%) it’s not a FM piece.
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Check the calibration and the IFR's should be in the area of 28-31 and the emulsion package should be rows of very small holes evenly spaced all the way down the tube.

Also FM went to a die cast design where the Carter was cast
 
Hysteric said:
Check the calibration and the IFR's should be in the area of 28-31 and the emulsion package should be rows of very small holes evenly spaced all the way down the tube.

Also FM went to a die cast design where the Carter was cast
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Here is what the Carter is…

IMG_0918.jpeg
 
That looks to be an early Carter.
 
Almost positive the competition series were all Carter, not Federal Mogul. I have two of the no-choke comp series 750s on my max xram.
 
From memory the 625SA were the FM Competition series
 
33IMP said:
Almost positive the competition series were all Carter, not Federal Mogul. I have two of the no-choke comp series 750s on my max xram.
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Pull one off and send it to me and I’ll test it lol. Just kidding. That’s a bunch of work
 
33IMP said:
Almost positive the competition series were all Carter, not Federal Mogul. I have two of the no-choke comp series 750s on my max xram.
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Is the number stamped on the foot of the carb 4760?
 
Hysteric said:
Is the number stamped on the foot of the carb 4760?
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I couldn't tell you. They are 250 miles away at the moment. I have a pic of the xram, but not anywhere near enough to read anything on the carb.
I have a pair of 3705s too, but there is literally NO numbers on them anywhere.
According to info I found , the chokeless 750 comp series should be 4762.
 
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The carb in post #55 is an original Competition Series AFB, model # 4759, 625 cfm.

For reasons known only to Carter, they introduced another lot of 'Competition series' AFBs in the emissions era which were not the same & had different jetting.
#4758 to 4762 were five comp series, from 500 to 750 cfm.
The 4759 came with 095 pri jets 086, #606 rods [ 061/071 & had no choke.
What is odd & might explain the power difference is the sec jets. The only difference between the 625 & 750 is the smaller primaries of the 625. Secs are the same & same boosters, but the 750 has 092 or 095 sec jets, depending on whether it has a choke.
 
33IMP said:
I couldn't tell you. They are 250 miles away at the moment. I have a pic of the xram, but not anywhere near enough to read anything on the carb.
I have a pair of 3705s too, but there is literally NO numbers on them anywhere.
According to info I found , the chokeless 750 comp series should be 4762.
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I have some very early ones without any numbers stamped on them also. The earlier correct 750's have a primary boost that is longer and places it at the correct height of the vena contractor so they flow.

After that Federal Mogul and Edelbrock made them with the shorter 600 booster. That's one of the reasons the 750 can have a stumble when going from transition to mains.
 
I'm not interested in participating in the carb science pissing match- but I will chime in that I have 2 seasons (probably 60-70) 1/4 mile passes running a pair of 800 AVS2s on my 440. I tune with an AFR gauge, vacuum gauge mounted on the dash connected to manifold vac, and reading spark plugs. I keep spreadsheets of changes and time slip performance. At the end of the 2023 season, I switched over to a pair of 650 DP ATM XRB series that they prepped for sideways dual quad service. Unfortunately, I only got 1 clean pass on the ATMs in October 2023, and my ET, mph, and 60ft were a little better than my best with the pair of Ebrocks. The next pass, I tossed a rocker arm and bent a pushrod, and that ended my season and I did a tear down and rebuild. (I suspect that my first pass might have had #6 cylinder rocker adjuster loose - and they let go second pass)

RMRW under hood.jpg


ATM 650 Pair.jpg



When rebuilding, I threw a stroker kit into the 440, so I'm now @ 505". I'm going to put the 2 ATM 650s back on it to start the dial-in process over again.

The main reason I switched from the Ebrocks to the Holley style carbs is the ease of adjust-ability with air bleeds, and availability of jets, power valves etc. We do drag-n-drives with this car, and we have tuned ourselves through a ****-ton of elevation changes, especially on Rocky Mountain Race week. The Holley Style is just easier and I think you can get the max out of them with less effort. I will save the AVS2s for a street cruiser - in that purpose, they are fine.
 
Bewy said:
The carb in post #55 is an original Competition Series AFB, model # 4759, 625 cfm.

For reasons known only to Carter, they introduced another lot of 'Competition series' AFBs in the emissions era which were not the same & had different jetting.
#4758 to 4762 were five comp series, from 500 to 750 cfm.
The 4759 came with 095 pri jets 086, #606 rods [ 061/071 & had no choke.
What is odd & might explain the power difference is the sec jets. The only difference between the 625 & 750 is the smaller primaries of the 625. Secs are the same & same boosters, but the 750 has 092 or 095 sec jets, depending on whether it has a choke.
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Is the other number next to the part number a date code? I’d like to know what era it’s from. I have no idea because my buddy bought it in 2015 and he was in California.
 
NBT,
I think it is the date code. Carter 4bbls generally were sequential with their numbering system. That jetting info I listed earlier comes from a 1971 Street & Strip annual that I have kept all these years, so I believe that those Comp Series would have been fairly new at that time.

Long boosters. Carter made 505 versions of the AFB, majority were production carbs. Some had long boosters, some had short boosters; some had the the booster leg pointing upwards, some had the leg pointing downwards. The up/down location of the venturi restriction was adjusted accordingly. Each carb was essentially custom designed for each engine. One of the sales 'features' of the Edel AFBs is the bullet nose on the pri booster nozzle. The Carter AFB on my 66 GTO had those.....
 
Bewy said:
NBT,
I think it is the date code. Carter 4bbls generally were sequential with their numbering system. That jetting info I listed earlier comes from a 1971 Street & Strip annual that I have kept all these years, so I believe that those Comp Series would have been fairly new at that time.

Long boosters. Carter made 505 versions of the AFB, majority were production carbs. Some had long boosters, some had short boosters; some had the the booster leg pointing upwards, some had the leg pointing downwards. The up/down location of the venturi restriction was adjusted accordingly. Each carb was essentially custom designed for each engine. One of the sales 'features' of the Edel AFBs is the bullet nose on the pri booster nozzle. The Carter AFB on my 66 GTO had those.....
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Tuner sent me a couple of links and we think it’s November 72.
 
I think it depends on who has worked on your Carter carbs, and i am not sure if the AFB is better or worse than an AVS , I have an AFB maybe 500 cfm, that was done for me that is probably the best carb i have ever ran. not sure how much different the car would run with a Holley based carb.
 
Wouldn't have been Steve Wann that did your AFB by any chance?
 
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