I have two AFB 3783's on the 31 and need to jet them down a bit. These are originally off a single carb 409 using 120/224 (.0995) primary jets and 120/159 (.089) secondary jets according to Carlos at BFIC. I currently have 120/163 primaries and 120/222 secondaries w/ one odd ball 120/256 jet on the drivers side carb. We were unable to cross reference the orifice size on the jets I have and was hoping some one may be of some help. The car is run pretty good right now, but its not perfect. It seems a bit fat all the way around and has an apparent flutter above 2500 which I am going to attribute to the odd ball jet --but I really dont know at this point--. Any help is greatly appreciated, as always.
Have you tried swapping out the metering rods?? I have always tried that first and seldom had to change jets.
Nope, but thats on my list. I am mainly trying to figure out where I stand as far as jet size since these are apparently jetted way down from the factory specs. Once I had that squared away I was going to buy all new jets and metering rods.
I think if it were me, I'd start with jetting and metering rods for a 600/625 Edelbrock (Pretty sure 3783's are 625 cfm). Looks like the .995 is pretty close to what the 1405 Edelbrocks use (.100). You could go with .070 X .047 metering rods (pn 1451) and .095 secondary jets (pn 1426), which is stock for the Edelbrock, and tune from there. Use the chart in the Edelbrock Owner's Manual to juggle your jets and metering rods. Otherwise it's pretty easy to get lost in the jet/metering rod selection. Larry T BTW, I've set up 2X4's on BBC, SBC, and SBF with low profile intakes and the only one I REALLY had to change jets/metering rods to get close was the 302 Ford.
Thanks Larry. That is what I am about to do. The 31 A has an xc-8 on it right now and I have an xf-8 for the galaxie. This is my first experience w/ dual AFB's and so far, none of the jet number I have correlate to anything I can find online. At least this is getting me primed for when Im actually ready to put the cross ram on the galaxie... I will take a look at the edelbrock sheet and let everyone know so that it can be referenced in the future and hopefully help someone else out. Thanks everyone.
The clone sheet will probably not be overly useful, as the air jets for the A/M carbs are totally different from the air jets used for O.E. applications. Suggestions: (1) Acquire a specifications sheet for the 3783s. These can be found in the Carter Master Parts books, and probably in a Chevrolet Factory Service Manual. (2) GO THROUGH BOTH CARBS AND RETURN THEM TO STOCK SPECIFICATIONS!!! Now you have a repeatable baseline. (3) See how the engine responds. Building the carbs stock may just solve your problems. Or maybe not. IF NOT: (4) Acquire a couple of genuine Carter Strip Kits for the 3783s. Original Carter number was 10-101. This kit was superceded by the more generic 10-201 (the 10-101 is more useful). Generally, Carter used the primary jets to get into a range that could then be fine-tuned by changing metering rods. Remember the effective metering area is the area of the jet less the area of the portion of the rod in the jet (both high vacuum and low vacuum steps). A few words on Carter jets: Carter had several different series of metering jets (at least 4 different series which were used on the AFB carbs). The earlier 2 series are not coded. You have to look up the number on the jet to determine the original diameter (however, remember that many hot rodders will drill jets). NEVER TRUST THE NUMBER ON A JET UNLESS YOU JUST REMOVED IT FROM A SEALED PACKAGE! The third series jets began with part number 120-350 (DO NOT USE THE FOLLOWING FOR LOWER NUMBERED JETS). The 120 is a code number for metering jet. For jets with number 350 and above the last 3 digits represent the jet diameter plus 0.300. Examples: 120-389 would be a jet of diameter 0.089 (389 - 300 = 89) 120-410 would be a jet of diameter 0.110 (410 - 300 = 110) The fourth series jet is the high step jet used for primaries on a few AFB's used on Chryslers, and the AVS series carbs. This series differs in that the subtrahend is 400. Example: 120-510 is a high step jet of diameter 0.110 (510 - 400 = 110) DO NOT INTERCHANGE THE HIGH STEP JETS AND NORMAL JETS. The high step jets require a different length metering rod. Jon.
The reason I suggested that the clone spec sheet may not be overly useful is very simple. From Carburetion 101: A carburetor is a device that meters and mixes air and fuel. Many tend to forget that a carburetor has air jets to meter the air. One can take 2 carburetors with exactly the same throttle bore, venturi size, metering jets and rods and have totally different calibrations if the air jets are different. And advice is always free (although some might say free is overpriced!) 573-392-7378 (9-4 Mon-Wed central time). Jon.
Yep, the air bleeds could be a different size and you might have to lean it out or richen it up. But you might have to do that if the carb has all "correct" parts in it too. It'll give you a base line. And it's gonna be a little easier to find current production Edelbrock pieces than it is to find obsolete Carter or REALLY obsolete early Carter parts. But I was forgetting that there are places (like you) that might have the 10-101 kits on the shelf. Sorry bout that. Larry T
Larry - please do not misunderstand my posts. I have no idea if we have any of the 10-101's left or not. I did check ebay this morning and there is a 10-201 kit there (with 9 bids so far). Any posts that I do on this forum are totally without any obligation. If I were trying to promote my product, I would not have listed the part numbers to look for. You are quite correct that the current production stuff is easier to find. And cheaper (ever hear the saying you get what you pay for?). Carter rods and jets were produced in the USA (St. Louis). Put a mic on a genuine Carter rod and it reads what it is supposed to read. We always try to check everything. We have have MUCH BETTER results with genuine Carter. And you are also correct in that the stock configuration may not be perfect on a different application. However, in 50 years of experience of working on carbs, I have found the factory engineers pretty well knew what they were doing. We always recommend building stock for a baseline UNLESS AN IDENTICAL SET OF CARBS HAS BEEN USED ON AN IDENTICAL ENGINE BY A TRUSTED FRIEND. In this case, one can start with a known calibration. Jon.
Jon, Believe me, I'm not picking on you. I am glad there are places (like yours) where you can go to get obsolete parts and advice. Please don't take it any other way. And like you, I've found that stock jetting is usually close on most of the intakes--tunnelrams, low profile, and single 4 bbl setups. I was just saying that you've got to have a starting point and parts to work with. And there are probably a lot worse places to start than the Edelbrock settings and their parts do fit. Also their chart does a lot to clear up what combos to use to go richer or leaner. Larry T
Went and got some jets today. I was glad to see Carlos at BFIC had NOS carter parts for me. The replacement jets I went w/ ended up being 398's (.098) on the primary and 283's (.083) on the secondary side. I already had the stock setup metering rods (220's) in both carbs. What I can say is that its smoother but still not perfect, still seems rich. From 2500-4000 it feels slightly out of sync, after that it seems to clear out. I'm still missing nearly 1500 rpm out of my powerband (spins up to about 6500 now), but I think that may be related to my valve adjustments. A few months ago I adjusted the valves and had to replaced some toasted points which is about when the carb's started giving me issues. Since then, I havnt been able to hit my usual 7500 shift point. It does not help I dont know WHICH cam is in the engine so I'm a bit in the dark w/ that. I started off w/ .016 lash to be safe then moved up to .018. The valves originally measured all over the place from .018 to .032. The one thing I have not done yet is actually measure the lash when hot, and thats next on my list along w/ possible replace the pushrods since they look a tad short from the wear pattern... Just wanted to give everyone an updated.
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