vacuum secondarys
Thread Starter
Melting Slicks
Joined: Jun 2004
Posts: 2,077
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From: westmoreland N.H.
vacuum secondarys
how can you tell if they are working correctly.i'm under the hood and try by going wide open throttle. but could not see them move.they are not binding, and seem to open by hand o.k. any ideas would help.... 
Drifting
Joined: Dec 2004
Posts: 1,345
Likes: 3
For a test, you can make the secondaries open mechanically by putting a small nut and bolt in the closing linkage of the butterfly. If you notice a big change in power then your secondaries are not working right. There are different springs that can be used to make the secondaries open sooner or later depending on your engine's needs.
The other thing you can do is remove the carb, open the throttle and blow air through the primaries (the side with the secondary vacuum actuator) and the secondaries should open.
The other thing you can do is remove the carb, open the throttle and blow air through the primaries (the side with the secondary vacuum actuator) and the secondaries should open.
Race Director
Joined: Jun 2000
Posts: 10,046
Likes: 675
From: FL
Originally Posted by StickShiftCorvette
For a test, you can make the secondaries open mechanically by putting a small nut and bolt in the closing linkage of the butterfly. If you notice a big change in power then your secondaries are not working right. There are different springs that can be used to make the secondaries open sooner or later depending on your engine's needs.
The other thing you can do is remove the carb, open the throttle and blow air through the primaries (the side with the secondary vacuum actuator) and the secondaries should open.
The other thing you can do is remove the carb, open the throttle and blow air through the primaries (the side with the secondary vacuum actuator) and the secondaries should open.
A Quadrajet is a mechanical secondary carb with a air valve that opens with demand. So, on a Q-Jet:
1) Make sure the choke is disenaged. You can push down on the linkage with a screwdriver to do this or just wait till the engine is warmed up.
2) With the engine not running, open the throttle fully.
3) Now, push down on the airvalve door and look at the secondary throttle plate. It should line up with the baffle in the secondary bores.
4) If the secondaries don't open, make sure that the secondary lockout is not still engaged. It is on the passenger side of the carb and is a pin controlled by the choke that stops the secondaries from opening. Just play with it till it is out of the way, then try again.
The airvalve only opens with demand which is one of the reasons that the Q-Jet works very well on the street.
