Upgrading A Quadrajet
Thread Starter
Racer
Joined: May 2013
Posts: 421
Likes: 6
From: Chicago IL
Upgrading A Quadrajet
I rebuilt my engine over the winter and wanted to reuse the Quadrajet I have. The only problem is what vacuum holes need to be plugged and which don't. Also, I need to convert it to an electric choke since there is a new intake - how do I do that and where do I find one? Anything else I need to know about? Thanks in advance for your help!
Melting Slicks
Joined: Oct 2006
Posts: 2,417
Likes: 336
From: Texas
Le Mans Master
Joined: Apr 2011
Posts: 6,284
Likes: 1,171
From: Hermosa
Delete the choke. Unless you're running it in the winter, then keep it.
I did my carb rebuild and mods using cliff ruggles book. You can get it at amazon for $20 or so. Do it once do it right and the q-jet will perform very well.
I did my carb rebuild and mods using cliff ruggles book. You can get it at amazon for $20 or so. Do it once do it right and the q-jet will perform very well.
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
You don't need to "plug any holes" on the Q-jet you have. And, you don't have to 'upgrade' it. All Q-Jets have the capability of flowing 750 cfm. All you need to do is swap rods/jets/secondary cam/hanger to tune it for your specific needs and hook it up properly to your throttle cable/linkage.
If it has a choke, just set it up right and it will not be a problem.
If it has a choke, just set it up right and it will not be a problem.
Le Mans Master
Joined: Apr 2011
Posts: 6,284
Likes: 1,171
From: Hermosa
The idle circuit is the one that will need modding for the vacuum developed by the engine depending on the cam.
Properly done it will start and idle without choke down to freezing temps without issue.
Melting Slicks
Joined: Sep 2004
Posts: 3,225
Likes: 667
From: Northeast
If you are serious about an electric choke, here are the instructions:
http://static.summitracing.com/globa...s/edl-1932.pdf
OP said he has a new intake and did engine work so retaining the old style choke might not be possible.
http://static.summitracing.com/globa...s/edl-1932.pdf
OP said he has a new intake and did engine work so retaining the old style choke might not be possible.
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Drifting
Joined: Mar 2011
Posts: 1,886
Likes: 9
I live in South Dakota and drive my vette April through December without a choke.
The idle circuit is the one that will need modding for the vacuum developed by the engine depending on the cam.
Properly done it will start and idle without choke down to freezing temps without issue.
The idle circuit is the one that will need modding for the vacuum developed by the engine depending on the cam.
Properly done it will start and idle without choke down to freezing temps without issue.
Exactly how?
And what about cold starts?
Le Mans Master
Joined: Apr 2011
Posts: 6,284
Likes: 1,171
From: Hermosa
The idle circuit is sensitive to idle vacuum. Less vacuum with a larger cam needs to be able to pull the fuel from the bowl easier. In my case I added more bypass air and enlarged the idle screw holes. These mods are explained in Cliff's book.
When it's cold (freezing or so) I crank until oil pressure is observed then pump the throttle twice and it fires up. Then keep it running for about 30 seconds to a minute with the throttle. after that the high speed idle portion of the choke will keep it running.
The choke itself is removed but I retained the high idle function for cold starts. That's the little bi-metal spring that holds the throttle up a little until it warms up.
When it's above 40* the high idle function is not even needed and it will idle after about 20 to 40 seconds of using the throttle.
Initial timing is very important for the idle. Mine is at 19*.
Also the correct vac can is very important. Mine will be fully retracted all the way down to 5" of vacuum.
This gives it a total of 36* of advance at idle. When cold and with low cylinder pressures the fuel has to be lit early to get it burning.
When it's cold (freezing or so) I crank until oil pressure is observed then pump the throttle twice and it fires up. Then keep it running for about 30 seconds to a minute with the throttle. after that the high speed idle portion of the choke will keep it running.
The choke itself is removed but I retained the high idle function for cold starts. That's the little bi-metal spring that holds the throttle up a little until it warms up.
When it's above 40* the high idle function is not even needed and it will idle after about 20 to 40 seconds of using the throttle.
Initial timing is very important for the idle. Mine is at 19*.
Also the correct vac can is very important. Mine will be fully retracted all the way down to 5" of vacuum.
This gives it a total of 36* of advance at idle. When cold and with low cylinder pressures the fuel has to be lit early to get it burning.
Drifting
Joined: Dec 2004
Posts: 1,714
Likes: 42
From: Austin Texas
i use a 1705xxxx q jet on my 74. I removed the hot air tube and blocked off that port on the intake. Then I converted to an electric choke like this one.
http://quadrajetparts.com/rochester-...ster-p-72.html
I only have one hose that goes to my carb, the PCV from the drivers valve cover. All the other ports have vacuum caps blocking them off.
I took the switched power for the choke by splicing into the wiper motor. I think its the yellow wire but double check that.
Cheers,
john
http://quadrajetparts.com/rochester-...ster-p-72.html
I only have one hose that goes to my carb, the PCV from the drivers valve cover. All the other ports have vacuum caps blocking them off.
I took the switched power for the choke by splicing into the wiper motor. I think its the yellow wire but double check that.
Cheers,
john
Thread Starter
Racer
Joined: May 2013
Posts: 421
Likes: 6
From: Chicago IL
Lol. Yeah, it is a little rough here and has been for too many years now. Good thing they just passed concealed and carry here 
7T1vette - I will need to plug a few as the intake is new as well as the water neck.
Thanks Karol!
Thanks johnt365 - that is what I am looking for.
7T1vette - I will need to plug a few as the intake is new as well as the water neck.
Thanks Karol!
Thanks johnt365 - that is what I am looking for.
Le Mans Master
Joined: Oct 2002
Posts: 7,098
Likes: 378
From: Las Vegas - Just stop perpetuating myths please.
I dont know if your '78 has a hot air choke or divorced choke but i think its hot air. The hot air choke can be easily converted to electric - the divorced cannot. U need a onversion kit like this: http://www.jegs.com/i/JET+Performanc...FU5lfgod7xkAOg.
But u can find them cheaper if u shop.
Hope this helps,
cardo0
Oooops, john bet me to it.
But u can find them cheaper if u shop.
Hope this helps,
cardo0
Oooops, john bet me to it.
Instructor
Joined: Mar 2014
Posts: 104
Likes: 0
From: Frankfort IL
I rebuilt my engine over the winter and wanted to reuse the Quadrajet I have. The only problem is what vacuum holes need to be plugged and which don't. Also, I need to convert it to an electric choke since there is a new intake - how do I do that and where do I find one? Anything else I need to know about? Thanks in advance for your help!