Quadrajet Build Thread

Longroof79

Rocket Powered Basset Hound
Oct 14, 2008
11,354
113
Gainesville, Fl
If you need a bolt on solution I have a nice 800 CFM Q jet from my 403.
Doug,
I was successful rebuilding the smallblock Q-jet that you sold me awhile back. It turns out, according to the model #, it came off of a 400 sbc. I also rebushed the primary throttle shaft. It runs like a top. and out performs the Holley that was on there previously. Thanks again.
 
  • Like
Reactions: 3 users

olds307 and 403

Geezer
Thread starter
Oct 14, 2008
7,471
113
Melville,Saskatchewan
So I decided to finish the base plate. I went through Cliff's book. He suggested .106 to .110" for idle air bypass and around .100" for the idle mixture holes. A 7/64" drill bit is around .105" with my digital caliper, it was close enough for both. I also measured the main air bleed in the air horn is around .070". The one in the main body is much smaller, a 1/16" bit won't fit, that measures around .058". I need to figure that out as it affects other measurements.
20210411_120406.jpg
20210411_120436.jpg
20210411_120628.jpg
20210411_120715.jpg
20210411_121645.jpg
20210411_121703.jpg
20210411_123704.jpg
20210411_123719.jpg
20210411_123735.jpg
 
  • Like
Reactions: 5 users

L92 OLDS

Comic Book Super Hero
Mar 30, 2012
2,644
113
West Michigan
Doug,
I was successful rebuilding the smallblock Q-jet that you sold me awhile back. It turns out, according to the model #, it came off of a 400 sbc. I also rebushed the primary throttle shaft. It runs like a top. and out performs the Holley that was on there previously. Thanks again.
So glad that worked out for you! It’s hard to beat a good Q jet.
 
  • Like
Reactions: 5 users

Longroof79

Rocket Powered Basset Hound
Oct 14, 2008
11,354
113
Gainesville, Fl
So glad that worked out for you! It’s hard to beat a good Q jet.
You're absolutely right. . It's always been a plan to put a decent Q-jet back on it. No regrets.
 
  • Like
Reactions: 4 users

Clone TIE Pilot

Comic Book Super Hero
Aug 14, 2011
2,672
113
Galaxy far far away
Okay, here is the rebuilding of the base plate. The stepped bit with the attachable collar makes drilling the correct depth easy. The hardest part is getting the bushings started straight. Red Loctite on the bushing and the screws for the primary throttle blades. Everything is now nice and tight without slop, phase one is complete. Next will be removing idle channel restrictions. Also a couple of pics of one of my 4 helpers, Dixie, the youngest Dachshund View attachment 172836 View attachment 172837 View attachment 172838 View attachment 172839 View attachment 172840 View attachment 172841 View attachment 172842 View attachment 172843 View attachment 172844 View attachment 172845

You have to be very careful about bushing the passenger side. The boss is very thin and prone to cracking after bushing. My first carb base plate cracked there after a few heat cycles. Its why J prefer to use Teflon strips to rebush Qjets. Passenger side does not require any drilling, only the driver side needs its stepped bord drilled a little deeper. Plus the Teflon strips act as seals too.

When bolting the carb back on be sure to use a thick mounting gasket. Torque the bolts to 144 in/lb, best to use a in/lb torque wench. After a few heat cycles check the torque of the carb mounting bolts. If they are 60 in/lb leave them alone. If less than 60 in/lb, then retorque to 96 in/lb.
 
  • Like
Reactions: 4 users

olds307 and 403

Geezer
Thread starter
Oct 14, 2008
7,471
113
Melville,Saskatchewan
I do have the thick base gasket. Hopefully there are no issues with cracking. I do have an extra base plate.
 

olds307 and 403

Geezer
Thread starter
Oct 14, 2008
7,471
113
Melville,Saskatchewan
So a review of Cliff's book made it clearer. The idle air bleed in the main body is close to .070" according to my digital caliper. The main air bled in the air horn is around the same. The one in the main body seems smaller then even my smallest 1/16" drill bit. The idle tubes are being stubborn, they will need some heat to come out.
 
  • Like
Reactions: 1 user

olds307 and 403

Geezer
Thread starter
Oct 14, 2008
7,471
113
Melville,Saskatchewan
Ok, more cleaning and finally got the idle tubes out and replaced with Cliff's custom tubes, I believe .039" is what he did up for me. I also tapped the air horn for the 3/8" plug Cliff sent. The APT was 9.5 turns from seated. My other carbs were around 10.5 to 11 turns, makes this even leaner. The APT is now notched and I can easily adjust part throttle with a small standard screwdriver, the car running or not. Also why are only tiny pics allowed, big time cropping or file is too large.
20210417_173544.jpg
20210417_173951.jpg
20210417_174057.jpg
20210417_174245.jpg
20210417_174335.jpg
20210417_174609.jpg
20210417_175039.jpg
20210417_175327.jpg
20210417_175529.jpg
 
  • Like
Reactions: 2 users

Supercharged111

Royal Smart Person
Oct 25, 2019
2,440
113
Colorado Springs, CO
My APT, which came from an 80s motorhome, was 1.5 turns out. It now sits around 4-5 I think. It'll be interesting to see what the wideband says whenever I get around to that. It's definitely still lean when cruising. I jetted down for altitude with math and it's not very happy.
 
  • Like
Reactions: 2 users
G-Body Performance Upgrades

GBodyForum is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to amazon.com. Amazon, the Amazon logo, AmazonSupply, and the AmazonSupply logo are trademarks of Amazon.com, Inc. or its affiliates.

Please support GBodyForum Sponsors

Classic Truck ConsolesDixie Restoration DepotMike's MontesP-S-TSouthside Machine PerformanceUMI Performance

ContactAdmin@GBodyForum.comfor info on becoming a sponsor