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Old 12-19-2010, 12:04 AM
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Newbie with Quadrajet Has Questions

Hi all, hope you can help me with a truck I inherited from my dad. It's a 1981 Chevy Scottsdale. The original 305 and Saginaw 3-speed have been yanked long ago in favor of a SB 350 and B/W Super T-10. It has been sitting now for at least 5 or more years. When I put it away it was running kind of "questionable." So I am going through the truck and starting with a carb rebuild. I am hoping someone can guide me as to the correct vacuum connections this Q-Jet needs to run properly.

For reference the Q-Jet serial is 17081200. And from what I can tell this means 1981, Chevy, Automatic transmission. Anyone care to add/correct that?

Here are some photos

Front of carb:

Back of carb:

Choke pulloff (?) doo dad:

Here is how they were connected:
#1: not connected / open air
#2: capped off
#3: connected to valve cover
#4: connected to vacuum advance on distributor
#5: connected to choke pulloff

Thanks for any input you can provide.


Last edited by Silver Surfer; 12-19-2010 at 12:14 AM.
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Old 12-19-2010, 11:57 AM
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Number 1 This goes to the vacuum break on some Quadrajets, when you start it, it closes the vacuum break so the secondarys can`t open, when you floor it and vacuum goes to zero the vacuum break goes back so the secondary butterflies can open.
Number 2 is a overflow/vent. It`s usually connected to the carbon canister.
It can be left open or capped.
Number 3 goes to the PCV valve in the valve cover.
Number 4 I believe is a manifold full time vacuum port (pulls vacuum at idle) can be used for a number of things, Vacuum advance, vent controls, etc.
Number 5 Another manifold vacuum port, can be used same as above, including choke pull off.
There is the port right beside number 6 that is another vacuum port, the threads being the obvious giveaway, this is used as the power brake booster vacuum source. Usually, on the small ports it doesn`t matter what they`re used for, some being manifold and some being ported. For example, you can connect the vacuum advance to any manifold source and it won`t make it run any different. Same goes for the Vent Duct controls.
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