What Carburetor for Factory 4-bbl?
Printed From: TheAMCForum.com
Category: The Garage
Forum Name: AMC V8 Engine Repair and Modifications
Forum Description: AMC-made V8 engine mechanical, ignition and fuel from basic repair to high-perf modifications
URL: https://theamcforum.com/forum/forum_posts.asp?TID=103969
Printed Date: Apr/16/2024 at 1:36pm
Software Version: Web Wiz Forums 12.03 - http://www.webwizforums.com
Topic: What Carburetor for Factory 4-bbl?
Posted By: javelinjason
Subject: What Carburetor for Factory 4-bbl?
Date Posted: Feb/10/2020 at 10:29am
|
Pardon my ignorance, but what aftermarket carburetors will bolt up to the 73 factory four barrel intake, without modification? Not sure I want to keep the Motorcraft carb on my 73 AMX. Also, does anyone have a source for the carburetor insulator/spacer? Mine was shot and I can't seem to find a replacement. I looked at the Trans Dapt carb spacers, but not sure which part number would work. ------------- -1972 Javelin SST -1973 Javelin -1973 Javelin AMX PC |
Replies:
Posted By: Heavy 488
Date Posted: Feb/10/2020 at 10:39am
|
I believe that is still the 4300 and not the later 4350 spread bore. In that case a Carter, summit or Holley bolts on.NAPA may list the original style insulator. |
Posted By: javelinjason
Date Posted: Feb/10/2020 at 10:48am
|
The intake is the 3217486 4bbl from the 73 AMX on the 360. ------------- -1972 Javelin SST -1973 Javelin -1973 Javelin AMX PC |
Posted By: Heavy 488
Date Posted: Feb/10/2020 at 10:55am
|
It's more than likely a 4300 that uses a more common footprint. I believe the 4350 came in later in the 70's. You can easily check images of 4300 or 4350 online and compare which model it resembles. |
Posted By: Sonic Silver
Date Posted: Feb/10/2020 at 3:40pm
Edit: I was thinking that I should clarify the above. Some of the bigger cfm carbs have primary throttle butterflies that may be too big to open over the front 2 holes in the stock intake. I think the holes may be 1-7/16 inch in the front and 1-9/16 in the back. I believe that most, if not all 600 cfm square bore carbs should work. A spacer should fix the problem. |
javelinjason wrote:Posted By: White70JavelinSST
Date Posted: Feb/10/2020 at 4:29pm
|
I have a 401 out of a 76 Grand Wagoneer, it has the spread bore setup. Not sure what year it started.
------------- 70 Javelin SST, second owner, purchased 1972 |
Posted By: BassBoat
Date Posted: Feb/10/2020 at 5:27pm
| Trans-dapt makes an adapter for the weird motorcraft spread bore used in mid 70's jeeps and most ford 460 applications. Inch thick aluminum from spread bore to square bore holley pattern' |
Posted By: FSJunkie
Date Posted: Feb/10/2020 at 11:58pm
|
I have a 1973 360. The stock carburetor is a Motorcraft 4300. It is square bore. The secondary barrels are a little larger and higher flow than the primary barrels, but it is still a standard square bore gasket and bolt pattern. The manifold is a standard square bore manifold. The 4350 is a spread bore unique from the Quadrajet. It may share a pattern with the Thermoquad, but I am not sure. The 4350 was introduced in 1974 or 1975. ------------- 1955 Packard 1966 Marlin 1972 Wagoneer 1973 Ambassador 1977 Hornet 1982 Concord D/L 1984 Eagle Limited |
Posted By: AlexK
Date Posted: Feb/11/2020 at 2:18am
| The 4350 was introduced in 1974, might be late 1973. |
Posted By: ramblinrev
Date Posted: Feb/11/2020 at 5:33am
|
4350 introduced in '75. Nothing wrong with a properly rebuilt 4300. RamairRick does a professional job on them. ------------- 74 Hornet Hatchback X twins (since 1977) 62 American Convertible (still worth the $50 I spent in 1973!) AMCRC #513, AMO #384 70 AMX 360 4-speed (since 1981) |
Posted By: 401MATCOUPE
Date Posted: Feb/11/2020 at 5:39am
|
What will fit is the question....Square Bore Holley like a O-1850 from the old days, Edelbrock AFB/Performer for a Holley Flange or a Motorcraft 4300..... ------------- Ross K. Peterson 68X,GoPac,343,AT,52A(1stCar) 68X,GoPac,390,4sp,52A 69X,GoPac,390,4sp,64A 70X,GoPac,390,4sp,87A,8 70X,GoPac,390,4sp,BBO,8 70 Jav SST,390,AT,BSO 74MatX,401,AT,Prototype 74MatX,401,AT |
Posted By: javelinjason
Date Posted: Feb/11/2020 at 8:05am
|
Thanks for all the input. I'm not too experienced with carburetors, and they can be intimidating to me. I was born into the fuel injection age. The plan was to rebuild the stock Motorcraft 4300, but if I decided to go aftermarket, I wasn't sure what would bolt on the factory manifold. I've seen various spacers and adapters available. I forget what the factory insulator thickness is now... it's been a few weeks since I took it off and measured it. I know TransDapt makes spacers, and I think that's the route I want to go (versus the stock insulator). The end goal here is to rebuild or improve the carburetor while keeping the factory cowl induction air cleaner. Maybe one day I'll switch it over to the Holley fuel injection.... but that will be a long way off. ------------- -1972 Javelin SST -1973 Javelin -1973 Javelin AMX PC |
Posted By: Heavy 488
Date Posted: Feb/11/2020 at 8:46am
|
You shouldn't need an adapter. Good carb ( at least to me) for a driver would either be an Edelbrock or a Summit. More of a turn key than a Holley. About how thick of a gasket/spacer are you looking for? Paper thin or one of the thick factory gasket isolators with grommets on 4 corners? I can understand being intimidated with a carb in th OBD era. Crack a book, there's plenty. |
Posted By: Sonic Silver
Date Posted: Feb/11/2020 at 9:23am
|
Posted By: javelinjason
Date Posted: Feb/11/2020 at 11:10am
|
I'll look into the Summit brand. Thanks! As for the spacer, I understand and appreciate the intention of the factory insulator. It was there to prevent fuel boiling in the bowls. I'd go with the stock height, just in the phenolic material. TransDapt 2446 or similar may do the trick. https://www.summitracing.com/parts/trd-2446" rel="nofollow - https://www.summitracing.com/parts/trd-2446 ------------- -1972 Javelin SST -1973 Javelin -1973 Javelin AMX PC |
Posted By: Sonic Silver
Date Posted: Feb/11/2020 at 11:18am
|
Posted By: Trader
Date Posted: Feb/11/2020 at 11:19am
| When you get the spacer, and I have not used that one, just ensure it is the proper ID's and align with the bores of the carburetor. Nothing like having one put on and the secondaries hang after going WOT. |
Posted By: javelinjason
Date Posted: Feb/11/2020 at 11:21am
|
They make an open square model too, no butterfly holes. I wasn't sure if that would cause turbulence issues or not though. ??? ------------- -1972 Javelin SST -1973 Javelin -1973 Javelin AMX PC |
Posted By: Heavy 488
Date Posted: Feb/11/2020 at 11:28am
|
I'd try to find a 4 hole myself. https://m.ebay.com/itm/Carb-Carburetor-Spacer-1-2-Phenolic-Insulator-4-Hole-Holley-Carter-Edelbrock-/222086905156?ul_ref=https%3A%2F%2Frover.ebay.com%2Frover%2F1%2F711-53200-19255-0%2F1%3Ficep_ff3%3D2%26pub%3D5574933636%26toolid%3D10001%26campid%3D5337590781%26customid%3D%26mpre%3Dhttps%253A%252F%252Fwww%252Eebay%252Ecom%252Fitm%252FCarb-Carburetor-Spacer-1-2-Phenolic-Insulator-4-Hole-Holley-Carter-Edelbrock-%252F222086905156%26srcrot%3D711-53200-19255-0%26rvr_id%3D2294981655880%26rvr_ts%3D354be2801700a68c95c4d2f1fffaa780&_mwBanner=1&_rdt=1&ul_noapp=true" rel="nofollow - https://m.ebay.com/itm/Carb-Carburetor-Spacer-1-2-Phenolic-Insulator-4-Hole-Holley-Carter-Edelbrock-/222086905156?ul_ref=https%3A%2F%2Frover.ebay.com%2Frover%2F1%2F711-53200-19255-0%2F1%3Ficep_ff3%3D2%26pub%3D5574933636%26toolid%3D10001%26campid%3D5337590781%26customid%3D%26mpre%3Dhttps%253A%252F%252Fwww%252Eebay%252Ecom%252Fitm%252FCarb-Carburetor-Spacer-1-2-Phenolic-Insulator-4-Hole-Holley-Carter-Edelbrock-%252F222086905156%26srcrot%3D711-53200-19255-0%26rvr_id%3D2294981655880%26rvr_ts%3D354be2801700a68c95c4d2f1fffaa780&_mwBanner=1&_rdt=1&ul_noapp=true
|
Posted By: javelinjason
Date Posted: Feb/12/2020 at 12:39pm
|
Thanks again for all the input. We decided to get a Summit 500 CFM M08500VS and a 1/2" Summit brand phenolic spacer. It's a stock engine, so I feel this will be comparable to the Motorcraft 4300 which flows 431 CFM. This will be fun! ------------- -1972 Javelin SST -1973 Javelin -1973 Javelin AMX PC |
Posted By: Sonic Silver
Date Posted: Feb/12/2020 at 12:58pm
I have a magazine that tested a high 500+ horsepower Chevy engine with everything from a 390 cfm carb up to a 950. There was very little difference between anything form 600 cfm on up. The 390 was 22 horsepower down at peak, which was about 6,000 rpm. I think the 500 would be fine with a stock engine. |
Posted By: javelinjason
Date Posted: Feb/12/2020 at 1:01pm
|
A quick google search showed the 4300 was 431 cfm. I didn't do much more research than that. He ultimately wants to go to EFI, so this is just 'for now'. Either that, or rebuild the 4300 and keep it stock. ------------- -1972 Javelin SST -1973 Javelin -1973 Javelin AMX PC |
Posted By: Ken_Parkman
Date Posted: Feb/12/2020 at 2:14pm
| For information the SAE AMC report rated the AMC AFB at 430 cfm, but this was at 1" hg test pressure or delta P. Todays industry standard for flowing a 4bbl carb is 1 1/2" hg. The conversion is the sq rt of the delta P, so the stock AFB would be rated at 527 cfm in todays world. I have had them all on the flowbench, and the 527 cfm rating makes sense. |
Posted By: FSJunkie
Date Posted: Feb/13/2020 at 12:51am
|
The 4300 came in several different CFM ratings. Ford used them on a variety of engines. ------------- 1955 Packard 1966 Marlin 1972 Wagoneer 1973 Ambassador 1977 Hornet 1982 Concord D/L 1984 Eagle Limited |
Posted By: AlexK
Date Posted: Feb/13/2020 at 2:13am
Thanks Ken, Do you have any figures about the difference between 4300 vs. 4350 Motorcraft?
|
Posted By: Ken_Parkman
Date Posted: Feb/13/2020 at 7:00pm
|
The 4300 is a bit bigger carb than the AFB, and the 4350 is the same as the AFB. My flowbench cannot accurately flow a carb because you need a monster flowbench with a lot of power. But I can turn it to 100% and measure a pressure drop, and it is repeatable, so I can tell if a carb flows more or less than another. I've had 30 carbs across the bench so I have a good data base. The 4300 flows noticeably better than the AFB, just a tiny bit less than a 600 Edelbrock. BTW a 600 Edelbrock is a lot smaller than a 600 Holley 1850.
|
Posted By: Sonic Silver
Date Posted: Feb/13/2020 at 7:10pm
|
Posted By: purple72Gremlin
Date Posted: Feb/13/2020 at 7:23pm
|
Posted By: Sonic Silver
Date Posted: Feb/13/2020 at 7:31pm
|
Posted By: PHAT69AMX
Date Posted: Feb/13/2020 at 8:30pm
|
On the now defunct other forum Ken Parkman was generous to have compiled and posted a bunch of flow info for a bunch of different carburetors. I found some of that now gone forum post using the Way Back Machine, and then Ken was kind enough to look for, find, and send me some more of his good info that was absent. So it is not my info and don't know if I should post it... -------------  Link to a http://www.youtube.com/watch?v=MySiKQsmWxU" rel="nofollow - Short YouTube Burnout Video |
Posted By: Ken_Parkman
Date Posted: Feb/13/2020 at 9:17pm
|
OK by me. Probably a really good idea, cause I read my chart wrong. And maybe you should not believe me! Sorry about that. The 4300 is actually bigger than a 600 Edelbrock, my mistake was reading the line with a stub stack. But they are very very close, along with the 625 BG. The 600 Holley 1850 is noticeably bigger though than all 3 of those. I've decided carb flow numbers are a bit of a marketing game - tracked a huge variation in 750 carbs, even within the same manufacturer.
|
Posted By: PHAT69AMX
Date Posted: Feb/13/2020 at 9:49pm
|
And this is maybe a little 'beyond' the original posted question, but what brand and size carburetor to use can be a loaded question... imho best for an individual to learn a little about the 'marketing claims' and their shortfalls, then make an individual informed decision... I focus on Butterfly and Venturi Diameters more that claimed CFM Ratings. This is the part saved as text from the now defunct other forum, then after that is an image file of the chart Ken Parkman compiled:Ken_Parkman Carb flow test 02/09/08 at 22:39:45 For various reasons there seems to be a lot of carburators around here right now, so I decided to put them all on the flow bench for comparison. My flowbench cannot effectively measure a carb cause to do it right you need to have a bench that will suck the roof off the shop and has a direct power supply from the generating station. But what I can do is run the bench wide open and then put on different carbs and measure the pressure drop, and then I can compare one to another. I could check an individual barrel, but that takes fixtures I don't have and can't be bothered making. As you know there is way more to carbs than flow - a point that has really been hammered home to me with some dyno and track testing. Also as you know factory ratings are pretty much meaningless cause they are marketing more than anything. So this is an effort to see how much some manufacturers are exagerating. Do not use this data to say one will make more or less power; it's only for interest. So here is the list of different carbs and their ranking flow wise, smallest to largest: Rank/Carb/part number/rating/comments 1 Edelbrock 1405 600 2 Holley 1850 600 Significantly more flow than Edelbrock 600 3 Q-jet ? ? Secondary air flap has a stop to limit opening 4 Holley 4777-2 650 5 Edelbrock 1407 750 Slightly more than 650 Holley 6 Edelbrock 1813 800 Big improvement over 750 Edelbrock 7 Q-jet ? ? Secondary air flap opened noticably more than above Q-jet 8 Holley 4780 800 Same dimensionally as a 750, but this carb had a slight TB mismatch. 9 Holley 3310 780 Factory GM original 3310, down leg booster 10 Holley 3310-2 750 Strait booster than above, flows a little better but close 11 Pro-Systems XC ? Built for a mild 327 Chev, noticably more flow than above Holleys 12 Holley 4781 850 No choke plate 13 Holley 80514 1000 Annular booster carb, very small flow difference from 850 14 Pro-Systems XE ? Down leg booster, very significantly more flow than 1000 Holley A couple of comments: The Edelbrocks flow significantly less than the same rated Holley Holley plays games with flow ratings. Yes a 750 Holley flows more than a Holley 800. I've heard it before, but this seems to confirm a 850 holley is a lot bigger than a 950. Dimensionally the 850 is bigger. The 850 with no choke and a stubstack was essentially identical to the annular booster 1000. Stubstacks noticably improve the flow. A fancy cnc milled 2" spacer slightly improves the flow. The Q-jets were flowed with an adapter that slightly restricted the flow, but calibrating with a holley says the resriction was not much. I'm going to try to get a few more carbs to add to this list, including a factory AFB and Motorcraft. ------------------------- Ken_Parkman Re: Carb flow test Reply #6 - 02/10/08 at 17:10:59 Trying to find some stock AMC stuff, just don't have any here! I hope to score a stock AFB and a 4300 to test, I'll post if it happens. What Reagam said is important. A high flow carb is no good if it can't properly atomize fuel at a low delta pressure. Only take this data as an interesting comparison. Of course a really good carb is both high flow and can properly control the mixture at a wide rpm and load range. A simple flow test cannot tell this. -------------- Ken_Parkman Re: Carb flow test Reply #8 - 02/16/08 at 18:22:16 Those were 2 different stubstacks, both K & N. One is very old (been through a carb fire) and has been modified to better fit the 850, which seems to have a different height air horn then the stubstack was designed for. The other is an almost new one made from a different plastic and fit the 750 very well. Both noticably improved flow, but clearly the bigger 850 really liked it, the flow was well up. The spacer is a really trick cnc milled 4 hole translating to an open with a nicely faired 'bullet' in the center. But now that I am carefully looking I find it has slightly small bores on the 4 hole part. I'm gonna fix that and try again. Just scored a couple of Demons, a good prepped dyno 750 holley, and a stock AFB. Hope to have a Motorcraft and a few more Holleys tomorrow. Will post info ------------- Ken_Parkman Re: Carb flow test Reply #14 - 04/28/08 at 02:32:16 I FINALLY managed to score some stock AMC carbs and get all the data together. I've had 29 carbs accross the flow bench and it is an interesting exercise. I've learned carb flow numbers are a game. Do not assume a carb is bigger because it it rated higher. The highest flow 750 carb was 150 cfm better the lowest flow 750. A surprise is the stock Motorcraft 4300. I scored a OWA4-S, and it's surprisingly good flow wise. It looks crappy, but flows a tiny bit better (not enough to give a number) than a Demon 625 or an Edelbrock 600, both of which are pretty much the same. A Holly 600 is about 40 cfm better than the BG and the Ed. The stock AMC AFB (tested # 4664) is about 40 cfm less than the sam BG and Ed Carbs. The Ed 600 is an AFB and is basically the same carb as the stock AFB. It has the same bore's and venturi's, but the Ed has 1/2 throttle shafts and a little aerodynamic fairing to account for the 40 more cfm. The 4350 Motorcraft is the same as the stock AFB. I scaled the carbs on a 0-100 scale, and here are the small carbs Edelbrock 750 (1407) - 71 Holley 700 (4778) - 71 Holley 650 (4777) - 69 Rochester Q-jet (xxxx) - 67 (small one) Holley 600 (1850) - 65 Motorcraft 4300 (xxxx) - 61 (OWA4-S) Barry Grant 625 (xxxx) - 61 (Road Demon) Edelbrock 600 (1405) - 61 Carter AFB (4664) - 57 Motorcraft (4350) - 57 --------------- (4) MORE POSTS ON PAGE 2 -> BUT NOT ON WAYBACK MACHINE ! ------------------- -> ( 14 ) POSTS REPLIES ON PAGE 1 - SAVED HERE ALL post BY KEN PARKMAN ( 4 ) MORE POSTS ON PAGE 2 -> BUT CARP! I CAN'T FIND! NOT ON WAYBACK MACHINE ! -> Today, Wed, Feb 20, 2019 -> post on Billd Forum to Ken Parkman asking for missing text ----------------- crap ! PAGE 2 WAS not SAVED BY WAYBACK MACHINE ! And this is the image, hope it is legible, have yet to take time to type it up:  ------------- Link to a http://www.youtube.com/watch?v=MySiKQsmWxU" rel="nofollow - Short YouTube Burnout Video |
Posted By: javelinjason
Date Posted: Feb/14/2020 at 7:45am
|
This is all far and above my original question, but it has turned out to be a great discussion! If this were more of a performance build, I'm sure we would have went with a different CFM rated carburetor. Maybe for the next one! ------------- -1972 Javelin SST -1973 Javelin -1973 Javelin AMX PC |
Posted By: PHAT69AMX
Date Posted: Feb/14/2020 at 2:13pm
|
It you just want a new bolt on carburetor that works - the Summit Brand Crabs people say are good. They are just a rebranded Holley design from the 80's, and are low cost. If you are ok with rebuilding and tuning a carb, get a used holley list 1850 for $50 off MarketPlace. Getting pieces and parts and 'input', ha, for the 1850 Holley will be easy. All also available for the MotorCraft AutoLite but less readily, maybe more costly, a new float for that is high dollar from what I understand, and the Dual Inlet Needle set-up can be tricky to get correctly set-up, some web sources show blocking off the 2nd Inlet Needle. For the Spacer, finding stock will be less than easy. Aftermarket carbs most likely will already have the needed hose connections that were in the stock spacer since the stock MotoCraft AutoLite lacked them. Square Flange 4-hole Carb Spacer of a material, brand, height, of your choice, some folks even make them out of wood at home. ------------- Link to a http://www.youtube.com/watch?v=MySiKQsmWxU" rel="nofollow - Short YouTube Burnout Video |