3269 AFB Calibration

[Greg S.]

Help from all the carburetor wizards out there.

I am in the process of restoring a correct 3269 AFB carb for a 1962 340 SHP that I purchased for my 340 HP 62.

My question revolves around calibrating with jets and metering rods. The primary jets I removed measure .104, which is to spec. The metering rods I removed are part #16-205 which I believe is correct. The book says the metering rod for a 3269 should be .069/.060. I measure the 16-205 metering rods from the carb to be .068/.054. I don't understand why I measure .054 on the second step instead of .060. I am using a dial caliper to measure. Edelbrock has metering rods that range from .057 to .075 for the top (cruise)step and .037 to .057 for the bottom (power) step. No where do I see a .060 bottom step. The closest I can come with an Edelbrock metering rod to the 3269 AFB specs of .069/.060 is .068/.057 or .070/.057.

I know the Edelbrock Performer carbs may have some differences compared to original AFBs but the stock calibration Edelbrock provides for a 1405 Performer carb (the closest equivalent to a 3269, 600 CFM moderate street high performance) uses jets and metering rods that are .100 for the primary jet and .070/.047 for the metering rods. This setup puts the carb in the mid lean/rich range for cruise and power. The tuning chart that Edelbrock provides shows a .104 jet and metering rods of .070/.052 to be very rich in cruise mode and slightly rich in the power mode for the Performer 1405.

The correct original spec for the 3269 seems to be way on the rich side for both cruise and power when compared to the Edelbrock Perfomer 1405. I know I can just put the metering rods back in the way I found them but I want to be able to tune the carb. I understand the way the metering rod jet combinations work on a theoretical level but I am confused about the differences in the original metering rod spec (.060 diameter power step) and the Edelbrock metering rod (.057 largest diameter and leanest power step). If I want to tune the carb it seems like the Edelbrock metering rods using a .104 jet can be sized for a leaner or richer cruise mode but only a richer power mode.

Has anyone used the Edelbrock jets and metering rods to come up with what you feel is an ideal cruise and power jet/metering rod setup for a 3269 AFB for a 340 SHP?

I am asking all this because my current setup is a 3721 AFB which seems to run rich in cruise mode. AC45 spark plugs are black carbon coated and seem to foul easily. I don't get the ideal tan colored deposit on the plugs.

[Clem Z.]

Re: 3269 AFB Calibration

the size of the air bleeds also enter into the equation. also the attitude enters into it also as carbs are calibrated for sea level and you want to reduce the area 2% for every 1500 ft above sea level. calculate the area of the jets and rods at differnt diameters and see what you can come up with

[Stuart F.]

Re: 3269 AFB Calibration

Greg;

The metering rods I am familiar with for 3461 and 3721 series AFB's are;
#16-389 = .060" x .069"
#16-124 = .063" x .069"
#16-204 = .063" x .073"

Both models, as you know, are very similar to yours as they were the series used from 1963 on up through 1965 on 327 ci Vettes. The variations are in jetting and air bleeds. I'm not familiar with the #16-205 rods, but it makes sense that the step difference you noticed (.057") would be possible. I don't think you are misreading your micrometer.

Stu Fox

[Clem Z.]

Re: 3269 AFB Calibration

F/M list a 16P-7060 which measures .070 X .060

[Timothy B.]

Re: 3269 AFB Calibration

Greg,

There were three revisions of this carburetor back in the day, primary venturies, choke setting and jetting/rods. Is there a A-B- or C before the month/year stamp in the front of your 3269. Check archives for discussion from years ago.

Your book may reflect only the last revision which sounds like the same as 1963,(3461). After 1963 the AFB is used only for the low hp cars and seems like it's leaned some. For 63 it's .104 and .069/.060 (16-389)

I agree with Clem in that if you want to compare today's available jets/rods with the Carter parts figure the sq.in. (area) and work from there also keeping in mind the air bleeds are probably a little different on the Edlebrock verses Carter.

Sounds like the smaller jet (.100) will be better to give a leaner mixture at power enrichment and be easier to tune with the edlebrock rod selection.

Does your car see a lot of idle time, that would explain the plug color.

[Greg S.]

Re: 3269 AFB Calibration

Answers to all poster.

Verne Franz referred to the 16-205 rods in a post in the archives which I have explored quite a bit. He indicated his Carter parts book dated Jan 62 listed the 16-205 .069/.063 rods for the 3269. My carb is a CD2 dated carb which is a later version- April 62 C modification (don't know what that is). I would guess that I probably idle the engine more than what would have been typical. Clem, I am in St Louis which ranges from about 300-800 feet above sea level. Can you still buy metering rods from Federal Mogul? I have been on their web site but can't find any info on carb parts.

My metering rods may have been Bubba'd over the years as the power step is definately .053. The secondary jets both measure approx. .068 but have two part numbers 120-181 and 120-368. Both are wrong according to archive data.

How do you measure the effective square inches of various jet metering rod combinations? What is the formula? I'm a salesman not an engineer.

I may just start with the Edelbrock .100 or .101 jets and metering rods if I can figure out the math. If anyone has already done this please post results.

Another problem I have been having regards the check valve for the accelerator pump nozzles. I have read that when rebuilding an AFB make sure that the valve does not fall out and go missing. Not much chance of that as I cannot get the check needle out of the main body. I have used penetrating oil, carb cleaner, air pressure and vigorous shaking but the check needle will not come out. Nor does it seem to move in the bore. How can I free it up to get it out and clean the passage and seat?

[Clem Z.]

Re: 3269 AFB Calibration

Answers to all poster.

Verne Franz referred to the 16-205 rods in a post in the archives which I have explored quite a bit. He indicated his Carter parts book dated Jan 62 listed the 16-205 .069/.063 rods for the 3269. My carb is a CD2 dated carb which is a later version- April 62 C modification (don't know what that is). I would guess that I probably idle the engine more than what would have been typical. Clem, I am in St Louis which ranges from about 300-800 feet above sea level. Can you still buy metering rods from Federal Mogul? I have been on their web site but can't find any info on carb parts.

My metering rods may have been Bubba'd over the years as the power step is definately .053. The secondary jets both measure approx. .068 but have two part numbers 120-181 and 120-368. Both are wrong according to archive data.

How do you measure the effective square inches of various jet metering rod combinations? What is the formula? I'm a salesman not an engineer.

I may just start with the Edelbrock .100 or .101 jets and metering rods if I can figure out the math. If anyone has already done this please post results.

Another problem I have been having regards the check valve for the accelerator pump nozzles. I have read that when rebuilding an AFB make sure that the valve does not fall out and go missing. Not much chance of that as I cannot get the check needle out of the main body. I have used penetrating oil, carb cleaner, air pressure and vigorous shaking but the check needle will not come out. Nor does it seem to move in the bore. How can I free it up to get it out and clean the passage and seat?

go here to save you doing the math. http://barrygrant.com/bgfuel/default.aspx?page=84 have not ordered carb parts for quite a while but i always ordered thru my auto parts. go down to the bottom of the page, "area of nozzles and jets".. there is a passage hole at the bottom of the pump well and using a air pressure try and blow out the check valve. hold your hand over the part or you will be looking for it on the floor.

[Greg S.]

Re: 3269 AFB Calibration

Thanks Clem,

I did use air pressure through the pump orifice and it would not budge the needle. I don't know how it can be so stuck. I may have to drill into it and pull it out with a tap. Ill soak it some more before I do anything so drastic.

I did a spreadsheet showing the % change from stock calibration using available Edelbrock jets and rods. See the attachment below. If I did the math right it looks like a .100 jet with .062/.052 rod a .101 jet with .065/.057 rod or a .104 jet with .070/.057 is close to the stock 3269 calibration.

I think I will try the .101 jet with .065/.057 rods. This combo makes the cruise calibration 1.3% leaner and the power calibration 3.7% leaner.

[Clem Z.]

Re: 3269 AFB Calibration

Thanks Clem,

I did use air pressure through the pump orifice and it would not budge the needle. I don't know how it can be so stuck. I may have to drill into it and pull it out with a tap. Ill soak it some more before I do anything so drastic.

I did a spreadsheet showing the % change from stock calibration using available Edelbrock jets and rods. See the attachment below. If I did the math right it looks like a .100 jet with .062/.052 rod a .101 jet with .065/.057 rod or a .104 jet with .070/.057 is close to the stock 3269 calibration.

I think I will try the .101 jet with .065/.057 rods. This combo makes the cruise calibration 1.3% leaner and the power calibration 3.7% leaner.

try tapping the top of the brass check valve with a small diameter punch and hammer. you can also try heating the area with a bernz a matic torch. nothing works better the "KROIL" penetrating oil

[Timothy B.]

Re: 3269 AFB Calibration

Greg,

1. Revision A corrected a stalling condition on stop and closed throttle turns by changing the primary clusters and metering rods.

2. Revision B is a change in the choke valve air gap at full choke to correct a over rich condition and choke coil is set to one notch lean so the choke opens faster. This revision includes revision A.

3. Revision C changes the air/fuel ratio at WOT and changes the metering rods from .069/.063 to .069/.056 which sounds like what you have. Also, changes the secondary jets from .0635 to .070. This revision also includes A and B above..

I think I would leave it alone and do a good rebuild making sure bleeds are open (check with small wire) and main body surfaces are flat top and bottom.. Use the .104 main jet and the metering rods .069/.053-4 and the .068 secondary jet.

The 120-368 is a good # for .068 jet, I am not sure about the 120-181#.

[Wes S.]

Re: 3269 AFB Calibration

Did you go to the edelbrock webstie and down load the owners manual for the performer series owners manul. It has a chart listing the rods and jets to accomplish different lean rich modes. Its tough to find the original Carter rods and jets, edelbrock makes the only parts that are easy to find.
Wes

[Greg S.]

Re: 3269 AFB Calibration

Yes I did download the Edelbrock charts. They are set up for the carbs they sell as a starting point. For instance the 1405 Performer starts with a.100 main jet and metering rods to match. It is difficult to use the chart for any other specific starting point. That is why I did the attached chart that shows relative areas depending on jet and metering rod combinations available from Edelbrock. I think I have a handle on where to start now.

[John F.]

Re: 3269 AFB Calibration

Greg, I'm in the process of tuning my Carter 3721sb AFB for my 65 327/300hp. I created an Excel workpaper that will assist me in calculating the effective area change arising from jet or rod swap. The workpaper allows you to enter various combinations of jet and rods and will calculate the % change in effective area compared to your existing set up. I think you will find it helpful.

If you need jets and rods, Summit racing carries the individual Edlebrock jets, rods and an assortment of step up springs. The stronger the step up spring, the more fuel you will consume.

I 've descovered NCRS will not allow me to upload an Excel file. If you e- mail me directly at difejo@optonline.net, I'll respond to your e mail and attach my file.

Good luck,