Quadrajet secondaries
Thread Starter
Instructor
Joined: May 2001
Posts: 229
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From: Yorktown Va Usa
Quadrajet secondaries
Ok im over 40 and more into cruising and doing the speed limit but on the sreious side my secondares do not kick in .I don"t want my corvette running like a Chevette either .Whats the most likely thing to look for .Does it sound like a vac problem ? :confused:
Le Mans Master
Joined: Sep 2000
Posts: 5,635
Likes: 4
From: Orlando Floriduh
Re: Quadrajet secondaries (hiyosilver)
Two things to check... First have a helper push the gas pedal down to the floor while you check to see if the throttle is opening all the way. there was a recent post on this.. the pedal assembly bends over the years and thecarb doesn't open all the way. Common thing on older C3's. Another thing to look at is the choke. If the choke is not COMPLETELY open there is a tang that locks out the secondaries. You can see it on the passengers side of the carb at the secondary shaft. After you check those, respost for more help.
[Modified by silvervetteman, 5:31 AM 1/18/2002]
[Modified by silvervetteman, 5:31 AM 1/18/2002]
Team Owner
Joined: Sep 2001
Posts: 30,958
Likes: 0
From: Middletown Connecticut
Cruise-In IV Veteran
Re: Quadrajet secondaries (silvervetteman)
i ditched the vac secondary Qjet for a custom mechanical secondaries Q-jet.. made a world of difference in performance :D and also gas mileage :cry
Race Director
Joined: Apr 1999
Posts: 11,520
Likes: 13
From: CORVETTE 77 385 C.I. TEXAS
Re: Quadrajet secondaries (Corzvette69)
FAST Q-Jet Fix by GANEY
A) Secondary air valve is held closed by vacuum when the engine is running at idle. If not, check vacuum hose on right (pass. side) front of carb.
B) Check that you have the right clearance on the rod that holds the sec. air valve closed w/ engine running, the clearance should be about .015-.020 or about the size of a pin.
This alone will fix many, you can try a little looser than this. This setting gets off slowly over time & adj. can unleash enough HP to make your car run like a Vette.
You may want to try TEST below before & after.
C) Check that throttle opens fully. Make sure your primary piston is not stuck down. Engine off, in the float vent tube, you can use a screwdriver to push piston down a little, should spring back up.
D) Adjust mixture, normally can not make too rich on 75-80. 75-79 Calif.
TEST Sec. You should be able to see the air valve at least starting to open by: Engine HOT, air filter lid off, pull back hard on throttle for a moment.
Note: Sec. will not open w/ engine cold unless sec. lockout on pass. side has been bent out of the way.
There is also an air valve spring adjustment.
Corzvette69
They all have mechanical secondaries, the air valve is vac..
A) Secondary air valve is held closed by vacuum when the engine is running at idle. If not, check vacuum hose on right (pass. side) front of carb.
B) Check that you have the right clearance on the rod that holds the sec. air valve closed w/ engine running, the clearance should be about .015-.020 or about the size of a pin.
This alone will fix many, you can try a little looser than this. This setting gets off slowly over time & adj. can unleash enough HP to make your car run like a Vette.
You may want to try TEST below before & after.
C) Check that throttle opens fully. Make sure your primary piston is not stuck down. Engine off, in the float vent tube, you can use a screwdriver to push piston down a little, should spring back up.
D) Adjust mixture, normally can not make too rich on 75-80. 75-79 Calif.
TEST Sec. You should be able to see the air valve at least starting to open by: Engine HOT, air filter lid off, pull back hard on throttle for a moment.
Note: Sec. will not open w/ engine cold unless sec. lockout on pass. side has been bent out of the way.
There is also an air valve spring adjustment.
Corzvette69
They all have mechanical secondaries, the air valve is vac..
