General Category > Quadrajet Carb Talk and Tips

17058213 carb

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mcx:
Yeah, those are SMAB type with "b" rods...they use the base plate APT system.
Main bleed .0465
IDCR .0465
Lower idle bleed .0595
Upper idle bleed .073
Idle air bypass .089
Secondary POE  .043
Primary jet 63
Primary rod 40b
Secondary rod CP
Hanger M

Cliff Ruggles:
What are you using the carb for?

The 1977-78 truck units with the SMAB set-up are emission calibrated and used very small main jets with "B" series primary metering rods. 

They calibrate similar to the later SMAB units but being smaller castings woln't need quite as much jet unless you open up the MAB's some (not recommended).

I would recommend if you are building one to free up the APT screw in the baseplate and get one of the external APT screws with a spring on it that I make here.  I can also supply the correct jets and metering rods exactly for the application if other than "stock".

Those are actually excellent units and I much prefer them to the 1970-78 large main airbleed divorced choke models, especially if they are being used on a "high performance" application.
 
I actually have a good supply of those carbs here and save them to replace early Chevy divorced choke units especially if the customer is missing a big block carburetor and can't locate an original.

Another very good starting point for Chevy divorced choke models is to find a 7029207 Service Replacement carb.  They were made in great numbers and plenty of them still around.  I either use those or the 77-78 SMAB truck units for most of the time when someone is looking for a Chevy divorced choke unit for an original set-up and have "warmed" over the engine a bit......Cliff

old cars:
Im setting up the carb for a mild 350 sbc approx 350 horse , about 211 duration @ .050
This would probably be first recipe in your book. Thoughts on jetting size?

old cars:
In response to mcx. All of my measurements seem to coincide with your post. Ill be opening up the holes under the idle mixture screws a bit.
My initial thoughts were to use 64 main jets jets with 36B rods . This would change the jet area from 1.8606 to 2.1991

Cliff Ruggles:
That's not what I would use in it.

First get the APT screw out of the baseplate, then call me at the shop and we can go over specifics and get what you need for it. 

As mentioned those are excellent units, they just need a little help in a few areas, jets, metering rods, PP spring, secondary metering rods, larger idle tubes and a few minor mods to get it set up for what you are doing.......Cliff

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