17085586 on a 396 with a bit of a cam....

[Dtrue2]

double post

[Dtrue2]

[77cruiser]

Here's some specs from one I did for a 385SB F/T cam 240@.050 108 LSA. Oh there we go that tight LS. It had about 11" vac. 700 rpm idle.
Idle tube .040
Down .059
IAB upper .070
IAB lower .062
SMAB .082
MJ 73
Pri Rod 50M
Sec Rod DH

[Papastoy72]

My engine is a 461 BBC, 10.0cr, same spec cam as yours except on 112 LSA. Vac is 15" Park, 11.5 Drive. Idles at 750rpm in drive very nicely.
Dual Main Air Bleed 800 carb.
Idle setup as follows:
Ijet = .035.
Upper Idle air bleed (air horn) .038.
Lower Idle air bleed .062.
IDCR = .048.
Idle screw hole .093.
Idle air bypass .138.

When I was running a Single main air bleed carb about 12 years ago (17082227), my Main jetting was as follows:
Mair air bleed .085.
Main jet .076.
Primary rods 52M (.036 tip).

According to my big Delco book, your carb is from Canada and was used on Big and Intermediate GM 305 cars (FWIW).

[Dtrue2]

Took it off and apart.
I don't have a full set of numbered drill bits so some are guesses based on what will and won't go.

Idle air bypass is .110 at bottom but a bit up from corner edge in throttle body/plate there is a restriction and it is less than .093
upper air bleed hole in airhorn right next to screw hole is .110
there is another hole (not sure if this is the lower air bleed that comes down/in at an angle also that is .110
main jet is #73
main rod tip is .026
secondary rod can be either CH ro CZ

not really sure where the lower air bleed is but if someone wants pics or can help figure that out that would be good.

[77cruiser]

Here's some good reading & has some good pics & diagrams.
http://www.wallaceracing.com/qjetidle.php

[rgalajda]

You need to use a magnifying glass to read the numbers on the primary rods and the secondary rods.

.026 is just the tip of the primary rod.


CH is .0570" , CZ is .0950" , big difference

Your carb looks like the one in this picture? Main air bleed arrows.

[Dtrue2]

[rgalajda]

These carbs were all over the place in regards to air bleeds, jets , and idle bypass air, over the years.
In the late 60’s main air bleeds could be as small as .040”
In 1970 Chevrolet switched to approximately .110 main air bleed and some of them had .134” idle bypass air. Idle air bleeds were all over the place. Idle tubes varied from low 30s to as large as .040”.

So large main air bleed requires larger main jet. Large idle air bleed requires larger idle tube.

In regards to your Idle bypass air . Some of those later carbs were drilled with a step in the baseplate, so the inner ( smaller ) step is where you meaure.
I would enlarge that to between .110 to .120”

Use your 73 main jets with the 43k primary rods. Adjust the APT to 3 turns up from bottomed to start.
You can knock the aluminum plug out so you can adjust when testing at cruise speed.

Use the CH .0570 secondary rods. But I think you will need a secondary rod approximately .0440 such as DA
Your mixture screw holes at .093 should be ok.

Test and decide if you need to go to .039” with the idle tube.

If someone would like to add to this , please do.

[Papastoy72]

I would follow what rgalajda recommends for the idle circuit. You may have to go larger than .120 for the bypass, that will depend on what your engine wants. As far as the main circuit, those carbs with the .110 upper and lower main air bleeds usually came from the factory with .077 main jets and around 48 to 52k primary rods. I would try 77 main jets with your 48k primary rods. Secondary recommendations are right on.