AFB different size jets
Thread Starter
Intermediate
Joined: Oct 2022
Posts: 31
Likes: 0
From: Bozeman,Montana
AFB different size jets
I am going thru my 64 300 HP 4 speed and undoing all the bubba items and have discovered the carb jets are different sizes left and right.
Carb is AFB 3721SA
Passenger side primary is 120-224 secondary is 120-175
Diver side primary is 120-3 ? something secondary is 120-194
Any ideas why?
Carb is AFB 3721SA
Passenger side primary is 120-224 secondary is 120-175
Diver side primary is 120-3 ? something secondary is 120-194
Any ideas why?
Last edited by TR64; May 20, 2023 at 10:08 PM. Reason: left out some info
Race Director
Joined: Jan 2003
Posts: 17,721
Likes: 3,706
From: Central Arkansas
Here is a chart for Carter jet sizes.
https://www.carburetor-parts.com/carter-jet-conversion
it’s a little unusual to have different jet sizes in an AFB on both primaries or on both secondaries - but not unheard of. Some carbs were fitted this way to deal with manifold imbalances in flow. If you have the Factory Service Manual you can look up your AFB if it’s original to the car and it will tell you the stock jet sizes. If it’s not the correct AFB for your car it may get a little more difficult as the old AFB factory service and parts manuals are pretty hard to find. Someone on here may have an early set. I would also check your metering rods as they are more than likely incorrect too if the jets have been played with a lot.
Mikes Carburetor Shop is a very good place to get AFB parts.
https://www.carburetor-parts.com/carter-jet-conversion
it’s a little unusual to have different jet sizes in an AFB on both primaries or on both secondaries - but not unheard of. Some carbs were fitted this way to deal with manifold imbalances in flow. If you have the Factory Service Manual you can look up your AFB if it’s original to the car and it will tell you the stock jet sizes. If it’s not the correct AFB for your car it may get a little more difficult as the old AFB factory service and parts manuals are pretty hard to find. Someone on here may have an early set. I would also check your metering rods as they are more than likely incorrect too if the jets have been played with a lot.
Mikes Carburetor Shop is a very good place to get AFB parts.
Race Director
Joined: Jan 2003
Posts: 17,721
Likes: 3,706
From: Central Arkansas
It appears that is a correct carb for your engine so here is some info in an old post that should help.
https://www.corvetteforum.com/forums...3721-info.html
https://www.corvetteforum.com/forums...3721-info.html
Pro
Joined: Mar 2020
Posts: 605
Likes: 300
From: Virginia Beach, VA conxefteris@msn.com
I was running a 3721SB on a 327/300 '64 using .104 primaries and it ran rich. I searched the forum and found this thread.
https://www.corvetteforum.com/forums...g-problem.html
When I went to .0995/.067 recommended by John Z it was much better.
As Dan said it's all about flow. If if runs well, I'd leave it alone.
https://www.corvetteforum.com/forums...g-problem.html
When I went to .0995/.067 recommended by John Z it was much better.
As Dan said it's all about flow. If if runs well, I'd leave it alone.
