quadrajet question, is mine backwards?
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From: Galveston... well, Santa Fe Texas
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quadrajet question, is mine backwards?
so my 1984 got swapped from Crossfire to a quadrajet by the DSPO.
did the secondary vacuum assembly get put on backwards?
as I understand it, the engine vacuum pulls the plunger in, which then pulls the rod, and opens the plates over the secondaries.
it appears, the way it's set up, that the vacuum would cause the secondaries to stay closed instead of opening them up.
as it sits
if I open the covers
please ignore the missing choke assembly.
did the secondary vacuum assembly get put on backwards?
as I understand it, the engine vacuum pulls the plunger in, which then pulls the rod, and opens the plates over the secondaries.
it appears, the way it's set up, that the vacuum would cause the secondaries to stay closed instead of opening them up.
as it sits
if I open the covers
please ignore the missing choke assembly.
Le Mans Master
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From: Oxford MA-----You just lost the game!!!!
No, that vacuum diaphragm has two purposes: it pops the choke open just a hair once the engine starts, and it keeps the flapper valve over the secondaries from opening too quickly, causing a bog.
Scott
Scott
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From: Oxford MA-----You just lost the game!!!!
With the engine NOT running, do this: push the flapper valve over the secondaries down, and twist the throttle linkage to full throttle (or WFO, as I like to call it
). You should be able to see the throttle plates opening in the secondaries, down in the throttle body. If they open, and the linkage from the gas pedal is adjusted properly, they almost can't help but work. Let us know how that works out for ya.Scott
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From: York Pa.
Well..probably the easiest way is to check if the arm is pulled in while running..the piece you pushed with your finger in on one of the posts..it shouldn't open while at idle..if you can move it then pull the vacuum line off the end of the diaphragm and see if vacuum is there..if there is vacuum turn off the car and depress the diaphragm in and put your finger over the hose end..it should hold vacuum..if it just pops back out then you need a new vacuum diaphragm ..
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So I ran the car, if I pushed the gas down, the secondaries did open. I didn't see any fuel come out of the secondaries, however.
Also, the plunger went in, and it took a little more pressure to manually move the arm.
Also, the plunger went in, and it took a little more pressure to manually move the arm.
Last edited by MonteHall; Jun 8, 2011 at 09:16 AM.
Burning Brakes
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From: Middleburg Florida
You won't see fuel coming out of the secondaries on a Qjet, they aren't like Holley double pumpers. First, I'd check to see if the vacuum pot is working correctly. Do this by seeing if it's holding (pulling the linkage in towards the pot) at idle. Like others have said, this thing stops the secondaries from opening too quickly, it doesn't open them. If it's working at idle, shut the engine off and make sure the linkage isn't holding the top "air valve" of the secondaries shut when there's no vacuum. Do this by simply pushing it open with your finger. It shouldn't take much effort to open the top of the secondaries. There are two parts of the secondaries, the air valve on the top and the butterflies on the bottom. Both of these have to work (and both are adjustable) to get the secondaries to open.
It might be worth getting a book on Qjets if you plan to keep the carb. They're very good carbs for the street when they're adjusted properly. Both Doug Roe and Cliff Ruggles have good books out about these things.
It might be worth getting a book on Qjets if you plan to keep the carb. They're very good carbs for the street when they're adjusted properly. Both Doug Roe and Cliff Ruggles have good books out about these things.
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yes. The plunger does get pulled into the pot at idle... to the point where the arm is at the end of the plunger plate-thing.
with the engine off, the valve on top of the secondaries takes no effort to open manually.
correct me if I'm wrong, but here goes: I start the engine, and the vacuum at low RPM keeps the plunger pulled in and doesn't allow the air valve to open. As I increase vehicle speed and RPM (flooring it) the vacuum on the plunger abates, and the airflow down the carb simply pushes the air valves open while driving?
with the engine off, the valve on top of the secondaries takes no effort to open manually.
correct me if I'm wrong, but here goes: I start the engine, and the vacuum at low RPM keeps the plunger pulled in and doesn't allow the air valve to open. As I increase vehicle speed and RPM (flooring it) the vacuum on the plunger abates, and the airflow down the carb simply pushes the air valves open while driving?
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Drifting
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From: Austin Texas
I know its extra money. However, I think you would really appreciate a base line chassis dyno run. Aside from telling you your hp and torque, most importantly it would show you your fuel ratio curve throughout the rpm range. Then you would know for sure if you had an issue and set out to correct it.
I guess you could also get a wideband Air/fuel gauge to do the same thing.
I guess you could also get a wideband Air/fuel gauge to do the same thing.
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From: FL
Q-Jets are not vacuum secondary carbs. They are mechanical secondary carbs with a air valve that opens as demand requires.
The actual secondary thottle blades are in the carb base plate. The air valve on top is held closed by the vacuum canister and will open at full throttle and when there is demand. As the air valve opens, it will lift the secondary fuel rods allowing fuel to flow into the secondaries. There is no accelerator pump on the secondary side.
Recommend getting Cliff Ruggles book on Q-Jets and getting familiar with how the carb operates.
The actual secondary thottle blades are in the carb base plate. The air valve on top is held closed by the vacuum canister and will open at full throttle and when there is demand. As the air valve opens, it will lift the secondary fuel rods allowing fuel to flow into the secondaries. There is no accelerator pump on the secondary side.
Recommend getting Cliff Ruggles book on Q-Jets and getting familiar with how the carb operates.
