quadrajet heat choke hookup? sb 400 - Chevelle Tech
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post #1 of 3 (permalink) Old Nov 10th, 06, 11:43 AM Thread Starter
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Jeff
 
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quadrajet heat choke hookup? sb 400

Hello,
I just got a 67 truck with a 72 sbc 400. The heat choke has been blocked off on the intake, someone made a plate. I purchased a rebuilt quadrajet for this motor. My question is ...is there any way to hook up a manual choke to the carb without messing up my secondary operation? or how would this heat choke setup be. i believe I have a heat riser piece that bolts to the intake. Is this just a vacuum line connection and be good to go? I pic of a heat choke setup on an intake would be great thanks. Thanks in advance
Jeff
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post #2 of 3 (permalink) Old Nov 10th, 06, 12:16 PM
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Mike
 
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Re: quadrajet heat choke hookup? sb 400

Is the intake the type that had a coil that was heated by the exhaust crossover? Is it the type that is called a "hot air choke"? The first type used a Quadrajet with a divorced choke. The second used one with a hot air choke.

If it's a divorced choke, no vacuum line necessary. Just get a choke coil and a choke rod.

If it's a hot air choke system, fresh air was drawn from a port on the airhorn of the carb (top section) through a vacuum line, through a metal tube heated by the intake, then the tube delivering the heated air was connected to the front of the choke assembly. If it's this type, you are in luck because you can convert it to electric choke very easily. Just put some RTV in the hole that provides the vacuum that draws the hot air - it's a tiny hole that you can see in the choke housing if you take the cover off. Then get a choke cap for a 1980+ Quadrajet that used electric choke. Run voltage to it from a souce that gets power only when the ignition is on. Put a vacuum cap on the port on the back of the carb that fed clean air to the old hot air choke, and you are done.

I have pics of both types on my signature. One carb is a 750 cfm Chevy that uses a divorced choke, the other is a 800 cfm Pontiac hot air style. Here is a pic to a 1976 Chevy hot air style choke:
http://www.geocities.com/unclepennyb...056502pass.jpg

For what it's worth, the electric / hot air style choke Quadrajets are nice, but in my experience, the old divorced choke style are hard to beat if you are looking to maximize fuel economy with an out of the box carb. My guess is that they richened up the A/F mixture to help lower Nox emissions some time around 1975, so the late 1960's or early 1970's Qj's are probably set up a little leaner. You can adjust the APT in the later ones to make up the difference, but it's a little bit of a hassle if you aren't into "tuning". Here's a link if you want to read more:

http://www.chevelles.com/forums/34-2002/72047-holley-vs-qj-results-post477716.html

Best Regards,

Mike

Last edited by Unclepennybags; Nov 10th, 06 at 12:46 PM.
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post #3 of 3 (permalink) Old Nov 10th, 06, 4:29 PM Thread Starter
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Jeff
 
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Re: quadrajet heat choke hookup? sb 400

Mike,
Thanks For the info, gotta to work now but Ill see what I can tear up tommorow!
Jeff
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