Tuning a Quadrajet carb???? [Archive] - Glock Talk

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vart
10-22-2006, 16:23
I have a Q-Jet on my `77 350 and it needs some work. Before I give up and buy a rebuilt one, I was hoping to try to tune it properly.

Unfortunately, nobody knows how.

I've taken to a couple of local shops, and posted on some Chevy forums, and nobody knows how to tune it. They all say they are tricky to tune and a great off-road carb when tuned.

I tried doing it the way I've done Holleys years ago: Turn in a mixture screw all the way, then back it out until the idle smooths out, then another 1/4 turn. Repeat for the other screw.

Didn't help much for mine:sad: .

Diesel Scout
10-23-2006, 00:56
Originally posted by vart
I have a Q-Jet on my `77 350 and it needs some work. Before I give up and buy a rebuilt one, I was hoping to try to tune it properly.

Unfortunately, nobody knows how.

I've taken to a couple of local shops, and posted on some Chevy forums, and nobody knows how to tune it. They all say they are tricky to tune and a great off-road carb when tuned.

I tried doing it the way I've done Holleys years ago: Turn in a mixture screw all the way, then back it out until the idle smooths out, then another 1/4 turn. Repeat for the other screw.

Didn't help much for mine:sad: .

I've never specifically delt with the quadrajets before, however I have always had trouble tuning carbs, in my case it's Holley's. I have a good friend who helps me out and I am convinced he sold his sole somewhere and was given the black magic to understand carbs. Anyhow, to the point. I recently have given it another try after reading online about tuning a carb by using a vacuum gauge. It worked quite well, and it might work for you. LINK (http://www.centuryperformance.com/vacuum.asp) Here is the specific guide I used when working with my last 2300, but there are plenty to be found online. This one just seemed more straight forward and user friendly. Hope this helps and good luck!

BPMACMAN
10-23-2006, 10:43
i may be able to help.i have built well over 100 quadra junks in my time. why dont you tell me exactly why you think it needs "tuned" and what your exact problems are.
bp

One Ragged Hole
10-24-2006, 13:45
I've always used a Vaccuum gauge to tune my Chevelle's (Holley) carb. Adjust the idle mixture screws to get the highest vaccum reading, it works just the same way with any carb. Start at about 1 1/2 turns out from "Lightly" seated. The spring tension on the Quadra Jet's secondarys can be adjusted to open them at the right time. Next should be the metering rods, but they are one of the last things to change.
O-R-H

vart
10-24-2006, 17:05
Originally posted by BPMACMAN
i may be able to help.i have built well over 100 quadra junks in my time. why dont you tell me exactly why you think it needs "tuned" and what your exact problems are.
bp
Black smoke on start up, idle gets rough, then smooths out, occasional miss.

BPMACMAN
10-24-2006, 17:53
if black smoke only on initial startup...suspect choke problem.1st check choke butterfly for binding,also check adjustment. also check choke pull-off.this diaphragm is hooked directly to choke linkage with a short vacuum line attached to rear. apply vacuum and verify that it will open the choke as well as hold vacuum. i have replaced more pull-off replacements than anything on these quadrajunks.

ElConquistador
11-02-2006, 20:48
Best way to "tune" your Quadraflush is with a Holley. Getting rid of that quadratoilet was the best thing I ever did for my old Blazer.

There are guys that swear by them and I guess when they work right they can run well and have good MPG, I've never actually witnessed this though.

elsolo
11-03-2006, 10:27
Tuning a carb is a lot more involved than just turning the idle mixture screws.
The black smoke indicates an over-rich condition at startup, which sounds more like a choke problem as the previous poster mentioned.