quadrajet carb
Thread Starter
Racer
Joined: Oct 2007
Posts: 431
Likes: 22
From: Chester Illinois
quadrajet carb
how can i tell if quad is really working. doesnt seem like it is kicking in. used to have an older pick-up truck with a quadrajet and you could tell it was working by the moan and instant acceleration. this is on a 81 vette auto. thanks, namvet6869
Safety Car
Joined: Sep 2005
Posts: 4,222
Likes: 643
From: Orange County Ca
Take off the air cleaner, start it in park, and rev it up. The secondaries should open. Works on a Q jet, not a Holley.
Also, very common for the throttle linkage to be misadjusted. Have someone put the pedal to the floor--with motor off, and look down through the top to see if the secondaries are fully open.
Also, very common for the throttle linkage to be misadjusted. Have someone put the pedal to the floor--with motor off, and look down through the top to see if the secondaries are fully open.
Melting Slicks
Joined: Mar 2006
Posts: 2,465
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From: Orange Park Fl
There are several things that could cause problems from a mal-adjusted choke locking out the secondaries to the carpet under the gas pedal being in a wad and keeping it from going all the way down. Check the throttle opening as described above and report back on what you find.
God bless, Sensei
Safety Car
Joined: Sep 2005
Posts: 4,222
Likes: 643
From: Orange County Ca
NO! If you did pull the throttle far enough to open the secondaries, you would not see it for the air valve! The air valve will only open under load, not just reving it in park.
This will work, but again, you have the air valve. As your assistant holds the pedal to the floor, open the secondary air valve (the butterfly on top of the secondaries) by hand. This will allow you to see if the secondary throttle plates are opening properly.
There are several things that could cause problems from a mal-adjusted choke locking out the secondaries to the carpet under the gas pedal being in a wad and keeping it from going all the way down. Check the throttle opening as described above and report back on what you find.
God bless, Sensei
This will work, but again, you have the air valve. As your assistant holds the pedal to the floor, open the secondary air valve (the butterfly on top of the secondaries) by hand. This will allow you to see if the secondary throttle plates are opening properly.
There are several things that could cause problems from a mal-adjusted choke locking out the secondaries to the carpet under the gas pedal being in a wad and keeping it from going all the way down. Check the throttle opening as described above and report back on what you find.
God bless, Sensei
Well, my Q jet must be that one special one that GM spent a zillion dollars on, specially for my car. Not. But, sitting on my driveway, the secondaries will partially open when the engine is reved up. Maybe 40%.They would probably open up all the way if I didn't mind running it open for longer than I'd like.
Notice I said partially open when reved in neutral. Mine does. The spring tension probably has alot to do with this on different carbs. If they open partially with a quick bip of the throttle, they should really open up when running at WOT for a longer period of time.
The lower blades are purely mechanical off the linkage. Easy to check, but, yes, you do have to manually open the upper blades when the engine is off, in order to see if the lower blades are fully open. But upper blades--the air valve--will open when running and parked, if the spring tension is adjusted correctly. Too much spring tension and it will open too late or not at all.
Last edited by Sayfoo; Sep 5, 2008 at 10:11 PM.
Racer
Joined: Oct 2005
Posts: 457
Likes: 1
From: Royal Oak Michigan
NO! If you did pull the throttle far enough to open the secondaries, you would not see it for the air valve! The air valve will only open under load, not just reving it in park.
This will work, but again, you have the air valve. As your assistant holds the pedal to the floor, open the secondary air valve (the butterfly on top of the secondaries) by hand. This will allow you to see if the secondary throttle plates are opening properly.
There are several things that could cause problems from a mal-adjusted choke locking out the secondaries to the carpet under the gas pedal being in a wad and keeping it from going all the way down. Check the throttle opening as described above and report back on what you find.
God bless, Sensei
This will work, but again, you have the air valve. As your assistant holds the pedal to the floor, open the secondary air valve (the butterfly on top of the secondaries) by hand. This will allow you to see if the secondary throttle plates are opening properly.
There are several things that could cause problems from a mal-adjusted choke locking out the secondaries to the carpet under the gas pedal being in a wad and keeping it from going all the way down. Check the throttle opening as described above and report back on what you find.
God bless, Sensei
Darrel1
Race Director
Joined: Mar 2008
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From: coffee
My CCC stuff is going in to a box in the attic.
Instructor
Joined: Jun 2005
Posts: 135
Likes: 0
Didn't see my reply post. I posted that I disconnected the rod that controls the air valves from the vacuum motor and now when I punch it, the air valves open immediately and the car has that familiar carburetor "WAAA" sound. Not sure what purpose the air valves serve (air/fuel mixture?). Anyway, if you put your car in Low and hold it at 20 MPH then punch it, you should feel and hear the secondaries kick in. My other cars have Carter AFB's and Motorcraft 4 BB's and they do not have those silly air valves and all sound great when opened up!
Last edited by Jon S; Sep 6, 2008 at 01:45 PM.
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Safety Car
Joined: Sep 2005
Posts: 4,222
Likes: 643
From: Orange County Ca
My experience with a non computer controled Q jet secondaries. The lower blades work strictly with the throttle linkage. Car running or not. No air, and of course no gas, will flow until the upper blades open. The air flowing through the carb creates a low pressure area which allows the gas to flow. You could say, the flowing air more or less sucks the fuel into the intake. With engine off, check to see that the lower blades open fully when the pedal is to the floor. You do have to open the upper blades manually. If not, adjust the linkage or brake pedal, etc. The upper blades will only open when the car is running. When they open is controled by spring tension on the blade shaft. For a performance engine, you can loosen up the spring tension, so that the air valve will open sooner. For economy, adjust the spring tenstion to open later. Open too soon and you are in for a major bog. Too late, and you lose perforamance, and the blades may not open fully. Read Lars papers that are availabe on this forum to adjust the spring tension. I adjusted mine on a hit or miss basis. Tighten or loosen the spring tension, then drive the car and note when or if the secondaries open. Adjust from there for YOUR preference.
Last edited by Sayfoo; Sep 6, 2008 at 09:25 PM.
Melting Slicks
Joined: May 2007
Posts: 3,246
Likes: 4
From: Bay Area CA
The spring adjust for the rear air door for the rear butterflys is here (see pic). There is a allen screw at the bottom (very small) that holds the small flat blade screw tight, after adjustment, from the bottom. Warm up car, take it out and run full throttle runs, adjust till the motor just stops bogging on initial stomp (tighter) 
initial adjsutment is about 1/2 turn after spring engagemant. (there's small spring it tightens-clockwise) C.
initial adjsutment is about 1/2 turn after spring engagemant. (there's small spring it tightens-clockwise) C.
Last edited by RunningMan373; Sep 8, 2008 at 07:12 AM.
Heel & Toe
Joined: Mar 2008
Posts: 21
Likes: 0
From: Lake Placid NY
Q-jet
I am waiting to read Lars' papers on the Q-jet......but after attempting to get mine dialed in by myself...I ended up disconecting the control rod to the vacum switch and adjusted the butterfly tension so they open with the secondaries. Now when I get on the gas there is a distinct difference when the 4bbl kicks in and car gets up and goes. I have had no ill effects with this....no hessitation when accelerating. Performance seems optimal at this point. Not sure what I can change after reading the Q-jet papers. Not too concerned obviously with fuel economy....car is only used about 4 months out of the year for nice day driving and I would rather have the performance than worry about mpg. I am assuming that the stock set-up is geared more for daily driving gas usage and not all out perfomance. Is this set-up going to do any harm....or OK to run this way if its dialed in and working????thanks....Peter
