quadrajet questions

J

jim83

Not-quite-so-new-guy
Mar 21, 2018
23
6
3
#1
Refresh my memory please- do the idle screws in the base plate turn in or out to lean the idle?


Also at what rpm does the idle circuit transition to the run circuit?

Carb is basic qjet- no computer contropls

thanks!
 
TURNA

TURNA

Geezer
Jul 24, 2009
6,316
7,994
113
Socialist NY
#2
Gently turn in all the way do not force them, then turn out 2 to 2.5 turns
 
MrSony

MrSony

Comic Book Super Hero
Nov 15, 2014
4,331
2,663
113
Des Moines, Iowa
#3
My jet idles best at 1.5 turns out. See what your car likes. Use a vacuum gauge and keep rpms about 600 or so in Park and adjust the mixture. Both screws should be set the same amount of turns from seated. Idle to the part throttle circuit is generally above fast idle..m somewhere between 1500 to 1800 give or take. Kinda depends on the carb.
 
Bonnewagon

Bonnewagon

Geezer
Sep 18, 2009
5,845
1,934
113
Queens, NY
#5
IN= Lean out
OUT= Richen
That's it right there. Every carb is different. Only a vacuum gauge can show you what your carb wants. I start with 4 or 5 turns out at a fast idle and that is very rich. I slowly turn each side in and as the engine responds I lower the idle. You try to get the idle down to whatever the engine likes best, say, between 500 and 800 rpm depending on your cam, and the highest vacuum reading at that idle speed. A stock cam should idle best around 650 with at least 20-22" vacuum. At 1000 rpm you are pretty much into the off-idle circuit. Once you find that sweet spot, with the engine off, you turn each screw in until they lightly bottom out counting the turns for each. Write that down and put it where you won't lose it. That is your go-to setting for future reference.
 
olds307 and 403

olds307 and 403

Comic Book Super Hero
Oct 14, 2008
3,775
1,648
113
Melville,Saskatchewan
#6
The late 70's Qjet's are extremely limited at idle, I found 5 turns ran best, highest vacuum only because the carb was too lean for the application. Now that it was reworked by Everyday Performance, I believe it is around 2 turns out.
 
Bonnewagon

Bonnewagon

Geezer
Sep 18, 2009
5,845
1,934
113
Queens, NY
#7
A good trick on the later Q-jets is to open the idle screw holes to .090" which is what they were before emissions. This works especially well when you have put a more aggressive cam in the engine. Unlike other modifications if it becomes no longer needed the screws can just be turned in to lean out the idle mixture as before.
 

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