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Setting the idle on my Q'jet

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billagroom

Guest
I rebuilt the Q'jet on my 79 it runs fine but on idle I can smell gas out the tail pipe. The manual is very confuseing turn in lo spd till engine drops turn back 1 turn. Can anyone clarify this for me?

Billagroom
 
Joined
Jan 1, 2002
Messages
7,246
Location
Washington, Michigan
Corvette
'67 Marina Blue Convertible
I've always found using a vacuum gauge to be a better approach than the "rpm-drop" method; connect a vacuum gauge to a full manifold vacuum source (like the fitting behind the carb on top of the intake), and adjust the idle mixture screws about 1/8-turn at a time, working back and forth between the two of them, to get the highest steady vacuum reading - you'll need to touch up the idle speed screw occasionally as you go to end up with the correct idle speed.
 
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SARGE81

Guest
q-jet

Billagroom,
Did you set the air/fuel mixture screws with a vacuum gauge? How many turns out from bottom are the mixture screws out?
Is the engine stock or modified?
Last question... are the throttle shafts good? Meaning no side to side "slop?" If they are sloppy you won't get a good setting. This is a common over looked problem with the Q-jet design.
Sarge
 
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page62

Guest
Can I add my 2 cents here? I'm having a heck of a time with the Q-Jet in my '79 too! No smog, true duals, lousy idle! In Park, it's almost 400-500 rpm higher than drive. And when I pull up to a stop, the rpms will subside (too low) after a few seconds.

Do I need adjustments, a new fuel filter, or a new carb?
 
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SARGE81

Guest
Page's Q-jet

Page, We need to know more about the car.
How many miles on carb and engine.
Does it have a radical camshaft?
Is there a lot of "slop" in the throttle shafts?
Have you done a complete tune up lately:plugs,wires,cap,rotor,checked timing,fuel filter.
This info can help us make a more educated diagnosis.
Sarge
 
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page62

Guest
Sarge, see my signature for the car's specifications. I'm getting all the things you listed done tomorrow -- already had the parts! I'll let you know the results.

But the carb looks tired -- I'm guessing it's been rebuilt at least once because I can see a new gasket. The bolts that hold the carb together have been torqued so tight they've chewed up a little of the metal beneath them. And the shafts do indeed feel "loose" (although I have no frame of reference on this one).

I'm thinking a new Edelbrock Q-Jet could be on my list...
 
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BobbyBJr

Guest
page62 said:
Sarge, see my signature for the car's specifications. I'm getting all the things you listed done tomorrow -- already had the parts! I'll let you know the results.

But the carb looks tired -- I'm guessing it's been rebuilt at least once because I can see a new gasket. The bolts that hold the carb together have been torqued so tight they've chewed up a little of the metal beneath them. And the shafts do indeed feel "loose" (although I have no frame of reference on this one).

I'm thinking a new Edelbrock Q-Jet could be on my list...

Well, you may have seen in another thread about my 75 that was acting about like yours. I had already made my mind up to send the carb out for a rebuild until the coil went bad. While trying to find the source of my problem, I changed the plugs, rotor button, condensor and point set (not original) and the coil and now the thing runs 200% better. I am going to let the carb wait awhile now and just drive the car.

Bobby
 
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page62

Guest
Bobby, yesterday I had did most everything you did...except the coil. Overall, the car runs better, but I still get a large difference in idle between Park and Drive -- although not quite as bad as before.

One person suspects the engine may have been rebuilt at some point...and possibly "breathed on" a little (cam seems a little lumpy at idle). I wonder if this has anything to do with it.

I'd be more willing to live with it, but the wife hates "standing" on the brake pedal at a stoplight!
 
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billagroom

Guest
Thanks folks I guess I need to get a vacume gauge. My car is full stock I have done a full tune and the shafts are not loose I'm sure I'm just not getting the jets right thanks for the Vacume advice.
Bill A Groom
 

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