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Old 06-28-2003, 09:31 PM
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Q-jet high idle

picked up a used q jet. it is actually an Edelbrock q jet 1904. anyway, with the idle speed screw backed all the way out it still idles too high. i don't have a tach on this rig but i would guess around a grand to 1200. the linkage is not binding and seems to come off the idle screw about the same as another q jet i have. aside from the high idle being anoying i don't think that my idle mixture adjustments will be accurate. anyone know what might be going on? i have a rebuild kit for it, but i just threw it on tonight for fun to see how it would do. my dad's 77 vette with a q jet does the same thing, idles at about 1100 and the idle screw is backed all the way off and not touching the linkage. whatcha think?

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Old 06-28-2003, 10:01 PM
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q-jets are natorious for leaking around the throttle bore axles. grab hold of the front one and push it in and out, at a 90 degree angle to the carb. it shouldn't move at all, but if it does it's letting in air and you will never get it to idle down. this is the most common problem I have ever had with them. I love the q-jet, but it really is a disposable carb. if this is your problem, it's a death sentence to the carb.
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Old 06-28-2003, 10:06 PM
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Might be a simple fix here... What base gasket are you using...? The thin paper one...? If so ditch it and get the 1/4" thick multi layer paper with reinforced bolt holes... The front vac channel area of the carb is not always covered by the contact with the intake manifold (thus a big vac leak causing high idle problems)... This is a problem when using an older Q-jet manifold with a later model of Q-jet carb...
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Old 06-29-2003, 12:51 AM
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Having throttle shaft bores wallered out is not a death sentence. Any good carb shop can install bushings which will make it like new. And when you install the return spring, hook it up in front instead of in back. This will cut down on the wear at the shaft holes.
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Old 06-29-2003, 09:18 AM
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Aaaah, never thought about the bushigs. and they can be purchased here:

http://www.carbs.net/quadrajet.asp

i'll have to do some wiggling and see if that is it. also i do have the thick gasket but that doesn't always mean its right. i switched from a 4MV (74-78) to a M4M (80-89) might be a slight diff in the bottem. i'll check it out today and post back. thanks,

jason
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Old 06-29-2003, 10:40 AM
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update:

i did have the wrong manie to carb gasket so i swapped in the correct one. it only helped marginally. i do have some play in my primary throttle shaft. however, i checked out the q jet i had on there before and it has just as much play or more and that carb idles down nicely. is there anything else that can cause this? thanks,

jason
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Old 06-29-2003, 05:04 PM
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Update #2:

found a rebuild kit that matched the gaskets on my carb and swapped em out. no change in performance. one thing i noticed is when the primary butterflys are closed they just bearly cover the off idle ports, where as on my other q jet they get covered more. i think this might be letting too much fuel in and causing it to idle higher. don't see anyway of adjusting this the butterflys do close all the way. is this something edelbrock might have done to allow for more fuel and air at idle with larger cams? as for driving and anything from off idle and up it does great.
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