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 QJ #17056230 setup 
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Joined: Sat Aug 24, 2013 7:57 pm
Posts: 155
Location: Frostburg, MD
Gents,

Before I became a member here and learned a wee bit, I did one of these carbs following a popular book [not the old Roe book]. I have three of these, so I checked out an unmolested one. They are '76 Cadillac carbs. I want to set one up for a 454 general use and tow '88 C3500 SRW pu truck. Stock engine at present. Will warm up later.

1st [upper] IAB .045" [in body]
Lower IAB .078"
IDCR .046"
IFR [jet] .033"

Idle bypass air holes .039"
Idle discharge holes .063"

Pri high speed enrichment discharge [in choke horn] .031"

Throttle plates closed gives apx .025" of slot under plates. Slot is "apx" .180" long. [a swag, did not remove butterfly]

Upper MAB [lid] .069"
Lower MAB .040"

"POE" well fill .039" [compensation jet]
"POE" discharge, below air doors .060" [capacity jet]

Secondary air bleeds .035" [bottom of tubes]

Air door 1.360" from back of choke horn to rear edge of door
Butterflies slightly shy of 90*

70 jets, 40L rods, H hanger, DH rods [.057" long]

-------
Plan - please critique;

Move 1st IAB to lid start at .042" [6-32 set screws]
Shrink lower IAB to .062"
.040" IDCR to start [8-32 set screws]
.028" idle jet to start [soldered to #8-32 set screws] - see response below

Idle discharge holes to .080" or so to start.
Bypass air holes to .060" to start [will have PVC]

MABs - set screws for upper? Start at .040" [too small?]
Leave lower MAB at .040"?

Clean well fill holes [comp jet] with .040"

Do tuner's secondary tube flip over, go .026" instead of current .035"

Start at #72 jet, # 42-44 rod, .053" sec rods.

Anywhere close?

Thanks.
Dave


Last edited by dave brode on Thu Sep 08, 2016 7:44 pm, edited 6 times in total.



Wed Sep 07, 2016 10:34 pm
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Joined: Sat Aug 24, 2013 7:57 pm
Posts: 155
Location: Frostburg, MD
Btw, I assume that the .035" secondary air bleeds are the reason the 1st carb barely responded to secondary metering rod changes as far as AFR changes? A .030" was not much richer than a .040" or even .053".

Dave


Wed Sep 07, 2016 10:41 pm
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Joined: Wed Oct 23, 2013 8:01 am
Posts: 113
You'll want 10-32 screws for the idle tube.


Thu Sep 08, 2016 8:11 am
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Joined: Sat Aug 24, 2013 7:57 pm
Posts: 155
Location: Frostburg, MD
77cruiser wrote:
You'll want 10-32 screws for the idle tube.


cruiser,

Yes, I see that #8 minor dia is too small. Do you know if the little sealing ridge on the body is damaged or cut away when using 10-32?

Any comment on my starting combo?
Thanks.
Dave


Last edited by dave brode on Thu Sep 08, 2016 7:45 pm, edited 1 time in total.



Thu Sep 08, 2016 10:13 am
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Joined: Wed Oct 23, 2013 8:01 am
Posts: 113
I think it was OK, haven't had any issues.
Combo looks good to me. Do you have a WB?


Thu Sep 08, 2016 11:03 am
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Joined: Sat Aug 24, 2013 7:57 pm
Posts: 155
Location: Frostburg, MD
77cruiser wrote:
I think it was OK, haven't had any issues.
Combo looks good to me. Do you have a WB?


Yes.


Thu Sep 08, 2016 12:57 pm
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Site Admin

Joined: Fri Feb 08, 2013 2:37 pm
Posts: 1744
You can use a .110" diameter drill bit to twist into and pull the brass cup restrictor out of the idle down channel. It helps to release the cup if you run the body under hot water or heat it some way, propane torch or electric heat gun.

I pull the brass cup restrictors and use them for main well bleeds in the 2 x .125 bleed carbs. You can make or modify a .093" diameter punch to have a very gently radiused flat tip with radiused edges to fit inside the cup. A gentle whack or two or three with your wee tiny hammer on your tiny wee anvil will shrink the hole.


Sun Sep 11, 2016 3:38 pm
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Joined: Sat Aug 24, 2013 7:57 pm
Posts: 155
Location: Frostburg, MD
tuner wrote:
You can use a .110" diameter drill bit to twist into and pull the brass cup restrictor out of the idle down channel. It helps to release the cup if you run the body under hot water or heat it some way, propane torch or electric heat gun.

I pull the brass cup restrictors and use them for main well bleeds in the 2 x .125 bleed carbs. You can make or modify a .093" diameter punch to have a very gently radiused flat tip with radiused edges to fit inside the cup. A gentle whack or two or three with your wee tiny hammer on your tiny wee anvil will shrink the hole.


Hey tuner,

I already did your .110" drill trick, they came right out unharmed. I have several of your posts saved, one with that trick. I'll get to work on it in the next couple of days. Does my plan look anywhere close for a starting point? [first post].

Thanks.
Dave


Sun Sep 11, 2016 6:49 pm
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Site Admin

Joined: Fri Feb 08, 2013 2:37 pm
Posts: 1744
Your proposal is good as a starting point. You will tune it with a WB so as long as it runs well enough to get on the gauge ...~~ You have the right idea about the large bleed in the secondary aspirator tube causing lean A/F and sluggish response to metering rod change, although depending on air-door spring windup the air-door may not be opening far enough to lift the rod to the tip with a short-tip rod (long taper). It will be interesting to see how your proposed idle system calibration works out.

This is a large primary venturi unit, eh?


Mon Sep 12, 2016 3:54 pm
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Joined: Sat Aug 24, 2013 7:57 pm
Posts: 155
Location: Frostburg, MD
tuner wrote:
Your proposal is good as a starting point. You will tune it with a WB so as long as it runs well enough to get on the gauge ...~~ You have the right idea about the large bleed in the secondary aspirator tube causing lean A/F and sluggish response to metering rod change, although depending on air-door spring windup the air-door may not be opening far enough to lift the rod to the tip with a short-tip rod (long taper). It will be interesting to see how your proposed idle system calibration works out.

This is a large primary venturi unit, eh?


Yes, large primary [all '76-'79 Cadillacs were, and, afaik, and all dual MAB].


The other ...6230 carb that I did was done before studying here. I ran all long power tip .026" sec rods, but I had the secondary aid doors opened too far, rear section vertical, and the butterflies open too far [vertical]. It also had various orifices done as per a popular book. It sucked gas like there was no tomorrow.


Mon Sep 12, 2016 4:48 pm
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