What would keep my secondaries from opening...
Thread Starter
Le Mans Master
Joined: Jan 2007
Posts: 5,485
Likes: 7
From: Peekskill NY
What would keep my secondaries from opening...
when the motor is fully warmed up, and the lockout is clear from the secondary lockout rod. I pulled the air cleaner off and pumped the throttle full and they stay shut. The carb is rebuilt (not by me) and was installed by the previous owner who is a mechanic. In a previous thread I posted , I mentioned that he said I needed the heat riser put on the exhaust for them to open, but if the engine is fully warm then that shouldn't matter, right? Where does the vacume come from to open them? HAs anyone had this issue and what did you do? I'm not ready to ditch the carb because the car runs good otherwise.
Glenn
Glenn
Drifting
Joined: Mar 2006
Posts: 1,526
Likes: 2
From: Oak Ridge NC
A lot smarter people than me will chime in, but I don't think you will see your secondaries open by flicking the throttle at idle. They start to open at just before WOT with load at about 3500 RPM if I am not mistaken. Sometimes you will feel the secondaries kick in, but if your carb is set up correctly, there should be a smooth transition from the primaries to the secondaries.
Thread Starter
Le Mans Master
Joined: Jan 2007
Posts: 5,485
Likes: 7
From: Peekskill NY
I use to have a 69 Impala with a 350/325 hp motor I put in, and the secondaries would open when I pumped the throttle full open by hand. They didn't open fully because I wouldn't hold the throttle open for very long, but they did open. That carb wasn't even the correct carb, the fuel line was straight, not at 45 degree angle like the chevy, had no choke and no lockout against the secondary lock rod and ran great. I definately remember hearing that great roar when they opened as well as felt it. So still puzzled. Again where's the vacume source that opens them? I've read a bunch of tech articles but still not clear on this.
Thanks guys for your thoughts and opinioins!
Glenn
Thanks guys for your thoughts and opinioins!
Glenn
Race Director
Joined: Mar 2006
Posts: 14,112
Likes: 28
From: Florida
The throttle plates (at the bottom of the carb) are opened by the throttle linkage only. This part is 100% mechanical.
Very simply:
With the secondary throttle plates open, the secondary airvalve, above the secondary throttle plates, is opened by the airflow passing across it.
At the same time, the area below the airvalve is exposed to lower pressure in the venturi area.
Both the Holley vacuum secondary carbs and the qjet are both known as "demand" carbs. They only give what the engine wants, but do it in slightly different ways.
Very simply:
With the secondary throttle plates open, the secondary airvalve, above the secondary throttle plates, is opened by the airflow passing across it.
At the same time, the area below the airvalve is exposed to lower pressure in the venturi area.
Both the Holley vacuum secondary carbs and the qjet are both known as "demand" carbs. They only give what the engine wants, but do it in slightly different ways.
Racer
Joined: Nov 2004
Posts: 432
Likes: 0
From: Granbury TX
Adjust secondary airvalve on QJet
Adjust the secondary airvalve tension by loosing the allen lock screw, it's up under the right side of the carb, and adjust the tension screw with a small screwdriver. See the below picture. I've taped the allen wrench to the choke so you can see where it goes, see it in the mirror. With a hot engine turned off, hold the throttle wide open and adjust so the flap pops back closed by itself. You'll have to drive it in between each adjustment until you get it just right for your engine. Too loose and it'll bog down, too tight and it won't open.
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Racer
Joined: Apr 2004
Posts: 370
Likes: 0
New England Events Coordinator
Need more info
Hi Lucky, the mysterious secondaries. On my 1970, 350 w/Quadra jet, there is a lock out control on the secondaries, appears to be controled in part by the mechanical choke but not completely. It appears there is something else that unlocks this. Can you explain further?
Drifting
Joined: Sep 1999
Posts: 1,970
Likes: 91
Right on noonie and lucky76. There is vacuum associated with this as well to keep the air valve from flappin in the breeze.
Although our 70's are a bit different in the setup, it works like lucky 76's photo shows. In the photo there's a long rod connected to the air valve plate. It runs forward to that dash pod with the vacuum hose in the front. As someone stated, it's supply on demand. Vacuum holds the shaft of the dash pod in. This holds the air valve blade closed. As you accelerate and vacuum lessens, that rod releases more and more until at WOT, there is no vacuum holding the rod in, hence the air valve is free to open fully.
Having said all that, you can disconnect and plug that vacuum line connected to the dash pod and see what effect that has on the secondary air valve. Ordinarily the dash pods leak, therefore don't hold vacuum, but is could still be an issue in your case.
BTW adjust that tension spring first. Get a small mirror to see what your doing. loosen the set screw and turn the adjusting screw counterclockwise until the spring end just touches the lever. Then turn,(I want to say 3/4 of a turn), and tighten the set screw. You can alter that adjustment from there.
Good luck Dennis
Racer
Joined: Apr 2004
Posts: 370
Likes: 0
New England Events Coordinator
secondary throttle plates
HI Dennis, the lock out control I was referring to is on the secondary throttle plates. This lock out is part of the assy that connects to the choke and primary airvalve assy. I am trying to understand this so I can assess if the secondaries function properly.
Cheers,
Cheers,
Drifting
Joined: Sep 1999
Posts: 1,970
Likes: 91
Le Mans Master
Joined: Nov 2004
Posts: 6,128
Likes: 21
From: North Alabama
Same on my 71. a Flull throttle "blip" in the garage and my secondaries open and start the "Wah...Wah" sound
Thread Starter
Le Mans Master
Joined: Jan 2007
Posts: 5,485
Likes: 7
From: Peekskill NY
You made that video for me and I've played around with it a bit but still no success. I bent the choke rod slightly so it would free up the lockout slightly earlierwhen the choke coil heated up. I'll try the spring tension adjustment and see if that makes a difference. I did check yesterday to see how tight or free it was and the flaps opened pretty easily by hand.
Is it possible they are opening but I'm unable to hear or feel it because the car is loud and the engine is not high horsepower. From what I've been able to find out it's somewhere in the 265 hp range but the owner that put this engine said he couldn't remember for sure. It just dosen't have the b*lls I was expecting. I figure if the secondaries did work I would definately feel a decient pull at WOT.
Glenn
Drifting
Joined: Sep 1999
Posts: 1,970
Likes: 91
Hey Dennis,
You made that video for me and I've played around with it a bit but still no success. I bent the choke rod slightly so it would free up the lockout slightly earlierwhen the choke coil heated up. I'll try the spring tension adjustment and see if that makes a difference. I did check yesterday to see how tight or free it was and the flaps opened pretty easily by hand.
Is it possible they are opening but I'm unable to hear or feel it because the car is loud and the engine is not high horsepower. From what I've been able to find out it's somewhere in the 265 hp range but the owner that put this engine said he couldn't remember for sure. It just dosen't have the b*lls I was expecting. I figure if the secondaries did work I would definately feel a decient pull at WOT.
Glenn
You made that video for me and I've played around with it a bit but still no success. I bent the choke rod slightly so it would free up the lockout slightly earlierwhen the choke coil heated up. I'll try the spring tension adjustment and see if that makes a difference. I did check yesterday to see how tight or free it was and the flaps opened pretty easily by hand.
Is it possible they are opening but I'm unable to hear or feel it because the car is loud and the engine is not high horsepower. From what I've been able to find out it's somewhere in the 265 hp range but the owner that put this engine said he couldn't remember for sure. It just dosen't have the b*lls I was expecting. I figure if the secondaries did work I would definately feel a decient pull at WOT.
Glenn
Old age. The memory is shot. Anyway, you can divide the operation,(or lack of), the secondaries into mechanical or vacuum. The vacuum side has been discussed. Engine vacuum corresponding to air valve opening. Also the choke operation locking out the secondary throttle plates.
One last thing, moving to the throttle side of the carb. What physically opened the secondary throttle plates is the rod linking the primary throttle lever to the secondary lever. It is possible there's an issue there but its easy enough to check. With the car not running, block the air valve open so you can see the throttle blades.Hold the vacuum lockout open. Then open the throttle linkage. At halfway or so the secondaries should begin to open. With the throttle opened fully the secondaries should be opened to a point just shy of vertical.
Le Mans Master
Joined: Oct 2001
Posts: 5,943
Likes: 3
From: Wildwood IL
If after adjusting your still unsure if they are opening, clip a small paperclip on the secondary linkage...go for a spirited drive...then check to see if that paperclip moved....and how much 
(Lars trick)
Eddie
(Lars trick) Eddie
Racer
Joined: Apr 2004
Posts: 370
Likes: 0
New England Events Coordinator
HI Dennis, yes this is the lock out that I referred to. This assy is triggered by the primary airvalve opening, is this correct. I like your idea on the paper clip, I will try doing this when we get a good weather forecast. The vette is still not out of hibernation for the winter.