[cees klumper]

It's really unpredictable whether, upon flooring the throttle, the second stage will or won't kick in. The difference is pretty noticeable, both from a sound and performance perspective. First I thought it was because of engine temperature but that does not seem to be the cause.
I've used the search but could not find an explanation. What could it be? Something electrical? When the engine is cold, manually moving the throttle does not open the second set of barrels.
Original '73 454 engine, don't know if the carb has ever been rebuilt or changed. The ignition has been upgraded I believe.

 

[theelcaminoman]

Theyres a thing on the left hand side of the carb that keeps the secondaries from opening if the engines cold (ie havent drove it for longer than 5 minutes). Its a smog thing. If youve been driving down the highway and kick it down, they should definitly engage.

 

[goodcruiser]

Are you talking about the actual secondaries or are you talking about the airvalve in the top of the secondaries?
If you're talking about the airvalve it has an adjustment on the passenger side,set screw I believe on top and a screw going in the side of the top plate of the carb for spring tension.If it is set too loose the valve will open too quick causing it to bog down,if it is too tight will won't open.Here's a website to check out.
http://www.73-87.com/7387garage/drivetrain/myqjet.htm
http://www.florida4x4.com/tech/quadrajet/index.php

 

[ccc]

check where the secondary air valvemeets the very back of the carb.if overtightened too many times the carb top will bind the air valve up.keeping it from opening.look in the area of the two very back screws that holds the top of the carb together.the metal can warp there around each screw.clean it with a file.lube all of your secondary linkage and pivots includeing the secondart lock out cam

 

[cees klumper]

Thanks very much for the suggestions - I will check things out with the secondary air valve etc and report back.