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73-87 Chevy _ GMC Trucks => Engine/Drivetrain => Topic started by: harkz28 on May 30, 2011, 05:15:34 pm
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How can I tell if the secondary's are opening on my carb. Its a 4 barrel Quadrajet on an 85 454. It does not seem to have the kick it should when you stomp on it. The carb was just rebuilt, I have revved it up from under the hood and when I open the throttle all the way for a quick blast I do see the large back plates move some. Any help? Also I need the idle kick up solenoid for the a/c. Its vacuum with two ports. I cant seen to find one?
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Try rock auto. You need to post more info on your carb. What's the casting #? Is it the stock carb?
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The idle compensators that I've seen are 12v, not vacuum. If yours is vacuum you could probably retrofit a 12v style easily. The secondaries have a tension adjustment on the air flaps to cause them to dump more gas if you need them to (tighter tension=less flap opening=richer fuel mixture).
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Hark, The secondary system on a Q-jet will not open much while sitting still. It is not a fully mechanical system. The air rushing over the upper flap at speed tries to open it...the tension spring & vacuum pull-off hold it shut until it's time to work (load sensitive) & then it falls/is pushed open. You only see a twitch from the vacuum draw the instant the lower butterflies open.
You can watch the linkage on the side of the throttle plate opening the secondary lever which should occur after about 1/3 throttle.
Once you verify that, loosen the tension on the secondary air flap (you can do a search for how to do it hopefully with pictures or I'll try to explain it) & drive the truck...once loosened too much, you will get a bog when you floor it (the dreaded Quadra-bog!)...tighten it up a little at a time until it's smooth. If you don't feel a change in any of the operation you will have to dig deeper. It should be real obvious your changing the opening condition. Any Questions, Just ask & I'll try to help. Lorne