73-87chevytrucks.com
73-87 Chevy _ GMC Trucks => Performance => Topic started by: micahadams on September 29, 2009, 10:36:22 pm
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I tried seaching but couldnt come up with much.
Anyone know a good way to make sure the vac secondaries are opening? I thought about a vid camera, a mirror or a midget to look while I am driving
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With the truck off, make sure the butterflies are opening. Pull the top off the air cleaner and look down the throat of the carb. Is it a factory air cleaner? Is it a Quadrajet? With my factory style air cleaner I can hardly hear it, but without the air cleaner on, it's easy to hear the Q-Jet "howl".
I'm sure there is a more "propper" way of doing it, this is just my sudo-redneck way.
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Take the air cleaner off and watch the rear butter fly. If it opens it is working.
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I like the midget idea best. Maybe a midget with a videocamera.
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Yea its a qjet. The butterflies are opening, but I am not sure of the air flaps. I guess it would run super rich it they didnt open. Thats why I want to phisically see them open with the motor running. I guess I could power break it and have a buddy look at the carb
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I guess I could power break it and have a buddy look at the carb
I smell a darwin award!
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If the secondaries on a Qjet are opening it is pretty obvious from the sudden surge of power and the sound.
What are you calling butterflies and what are you calling air flaps?
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Drive it hard in L2....the reason i say this is because it may be hard to the untrained driver to differentiate between stomping the gas and passing gear kicking in versus 4 barrels opening up. In L2, stomp the gas and you should be able to tell if the 4 barrels open. Also, reverse the air clearner top. You will be able to hear it when those barrels open up--the engine will sound soooooo goood.
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Yea I figures you would feel the surge. Thats why I am asking. I dont feel it. With the size differences in primaries and senondaies it would make sense that you would feel it.
I am calling the butterflies the plates closest to the manifold and the air flaps the top plates
I will try flipping the air cleaner top
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I realize Q-jets have a reputation for this but I would be unhappy with "feeling" my air valve open. To me it means something is out of whack with the primary side if the opening of the secondaries causes a sudden surge of power. And I don't believe for a second that this should normally occur on a Q-jet due to the disparity in size between the primary and secondary throttle bores. It should be smooth and seamless on any carb. But SgtDel is right I could always hear my air valve open. The exhaust note gets noticeably more guttural.
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do you have a digital camera with a timer? you'll be able to see when the flash goes off and judge if you timed the WOT well. Just sit that camera in a way it will point down to the carb.
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A rapidily dropping gas guage needle is a good indication the secondaries are engaged.
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I hope I'm not giving bad info., but I'm pretty sure the secondary throttle plate (butterfly) is mechanical on a quadrajet and the air flap has vacuum tension on it. The engine doesn't even have to be running to verify that the secondary throttle plates are opening. Just flip the air flap open with your finger and open the primary throttle until you see the secondary throttle plate open. If the engine is idling and you quickly flip the throttle to wot and see the secondary air flap open then its working. The secondary air flap is pulled open by vacuum when the secondary throttle plate opens. If all checks good I think the only other thing is making sure the throttle cable opens the carb. throttle all the way. I've read that the quadrajet "acts like" a vacuum secondary--but by definition is not.
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Thats true that the 2nds are mechaincal. Its about 2/3rds when they start to open. The air flaps have a time delay on opening. You can adjust for fast or slow they open. I want to make sure the air flaps are opening fully. I belive they take up to 2 sec at full throttle to fully open.
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Make sure your choke is releasing, there is a linkage that keeps the secondaries from opening until the choke is completely open, look on the pass side of the carb and you will see it. warm up your truck and see if its releasing. then drive it with the air cleaner lid flipped as said on here before, careful as this is addicting ..lol once you hear the sound its hard to stop..lol