Is this normal ?(Quadrajet secondaries)
Thread Starter
Drifting
Joined: Mar 2001
Posts: 1,411
Likes: 2
From: St. Louis, Missouri
Is this normal ?(Quadrajet secondaries)
When I floor the throttle on my stock '79 L-48, it pulls respectably until 3,000 RPM and then it REALLY starts to move (at least for a 24 year old V-8). Should the secondaries open right at WOT or is it normal for them to kick in at around 3,000 RPM?
I'm assuming that the Q-jet has vacuum-operated secondaries like a Holley 4160, not mechanical secondaries.
Thanks
I'm assuming that the Q-jet has vacuum-operated secondaries like a Holley 4160, not mechanical secondaries.
Thanks
Le Mans Master
Joined: Jul 1999
Posts: 9,206
Likes: 17
From: Sewell NJ
Re: Is this normal ?(Quadrajet secondaries) (Neo Fender)
What you're experiencing is normal because the Q-Jet will only give the engine what it demands. The Q-jet is actually a mechanical secondary with the secondaries governed by air flow. You can speed up or slow down the secondary opening rate by adjusting the spring on the air valve. This is on the right rear of the carb. You will see a small screw on the side and directly below it will be an allen nut. You can loosen the allen nut and turn the screw counterclockwise to speed up the opening rate. This should be done in stages until the carb bogs and then returned to the last good setting. The screw should only be moved slightly on each try like moving the hour hand on a clock from one hour to the other. You should read lar's papers in the corvettefaq on q-jets for a better explanation.
Safety Car
Joined: Mar 2000
Posts: 4,077
Likes: 27
From: Northeast South Dakota
Re: Is this normal ?(Quadrajet secondaries) (vettfixr)
Hey, that sounds like the problem I am having with my pickup. When I step on it hard so that the secondaries come on it bogs so bad it almost tries to die. When I had the top off it last time I set the secondaries up so that they fell open on their own, then I tightened them up until they just closed and called it good. Do you think I need to tighten that screw up a little more to prevent my bogging situation?
BTW, that is an interesting situation. It's an 86 K10 pickup. I bought it from the original owner. Since the day I bought it the secondaries were stuck shut, and the previous owner said it never did seem to have the right amount of power. After I had it for awhle (8 years:lol:) I decided to look into that one day when I was bored. The holes in the top cover that the rod that holds the secondary butterflies on goes through were not in a straight line. I had to file the middle holes a little bit oblong so that it quit binding up. :confused: I've never seen such a thing.
-Justin
BTW, that is an interesting situation. It's an 86 K10 pickup. I bought it from the original owner. Since the day I bought it the secondaries were stuck shut, and the previous owner said it never did seem to have the right amount of power. After I had it for awhle (8 years:lol:) I decided to look into that one day when I was bored. The holes in the top cover that the rod that holds the secondary butterflies on goes through were not in a straight line. I had to file the middle holes a little bit oblong so that it quit binding up. :confused: I've never seen such a thing.
-Justin
Team Owner
Joined: May 2001
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From: Exiled to Richmond, VA - Finally sold my house in Murfreesboro, TN ?? Corner of "Bumf*&k and 'You've got a purdy mouth'."
CI 6-7-8 Veteran
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St. Jude Donor '06-'10, '13
Re: Is this normal ?(Quadrajet secondaries) (Dalannex)
Tighten up the spring (screw) until that bog goes away. Most often it will be a stumble when the transmission shifts from 1st to 2nd and 2nd to 3rd.
Don't over do it, or you will stretch out and possibly ruin the spring underneath. That is a b*&ch to replace.
Don't over do it, or you will stretch out and possibly ruin the spring underneath. That is a b*&ch to replace.
Safety Car
Joined: Aug 2000
Posts: 3,943
Likes: 44
From: Florham Park NJ Port Credit Ontario
Re: Is this normal ?(Quadrajet secondaries) (Neo Fender)
I had to adjust the Secondary spring.
First, print out Lars' paper.
Second, make sure you put a small slotted screwdriver in the screw while loosening the allen screw. The spring is under tension and will spin loose if you do not hold it in place.
Third, do not over-tighten. You will bend the spring and replaceing the spring is not fun. Dont ask :banghead:
Once adjusted...no more bogs.
First, print out Lars' paper.
Second, make sure you put a small slotted screwdriver in the screw while loosening the allen screw. The spring is under tension and will spin loose if you do not hold it in place.
Third, do not over-tighten. You will bend the spring and replaceing the spring is not fun. Dont ask :banghead:
Once adjusted...no more bogs.
Tech Contributor
Joined: Aug 1999
Posts: 14,370
Likes: 6,361
From: At my Bar drinking and wrenching in Lafayette Colorado
Re: Is this normal ?(Quadrajet secondaries) (Stewart's74)
Set the spring to an initial wind-up of 3/4 turn. This will eliminate virtually all bogs. Then, back it off 1/8 turn at a time until the car bogs, and tighten up a tad again. Never tighten more than 1 full turn - I actually recommend 7/8 as a max setting. Most cars cannot handle anything looser than 1/2 turn without severe bog.
For specific instructions on setting this, drop me an e-mail and I will send you the excerpt from my Tuning Paper on setting up the secondary airvalve spring windup.
For specific instructions on setting this, drop me an e-mail and I will send you the excerpt from my Tuning Paper on setting up the secondary airvalve spring windup.
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Joined: Jul 2011
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From: Toledo Ohio
After further examination I feel like an idiot, The screw came loose (dont know when?) and let the spring unwind. I first noticed the stumble late last summer. I replaced cap, rotor, coil,and plugs. They had less than 10,000 miles on them but were 30 years old. When I replaced the acc. pump and float the pump seal fell apart too. Everything works now. Thanks for the info.
