More adjustment info
Date: Sat, 22 May 1999 00:05:51 -0500 From: Robert Lyssy (rlyssy at satx.net) Subject: More Q-Jet Adjusting Tips Following the information posted here concerning idle mixture and idle air bleed valve adjustment, I found the following to provide the best baseline for electronic Q-Jet adjustment for those like myself who had no prior settings to refer back to. Completely close both idle mixture screws (going clockwise), then back each one out two full turns. This should allow the desired 30 degree 6-cylinder dwell meter reading to be achieved with idle air bleed valve adjustment only. This was on my unmodified '86 SS. One and a half turns out on the idle mixture screws left the car a little flat on mild acceleration out of the turns. Moving up to the two full turns and leaning out with the idle air bleed valve improved the overall driving feel of the car, thru the turns and straightline. Idle speed was set a bit over 600 rpm in gear.
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Post from: Richard Kwarciany (kwar at FNAL.FNAL.GOV)
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Hi,
The "thingy" is the idle air bleed valve. It doesn't affect the
main circuit mixture, it only affects idle and part throttle. Think of the
idle adjuster screws as the coarse idle mixture adjustment, and the air
bleed valve as the fine adjustment. Connect an ignition dwell meter to the
mixture control test terminal. This is a green connector you'll find
sticking out of the wiring harness near the front of the carb. Start and
warm up the motor. Make sure it is at operating temperature. Adjust the
idle air bleed valve until the dwell reads 30 degrees on the 6 cylinder
scale. You may not be able to get the dwell to 30 degrees. If you can't,
and you've made changes to the motor (cam, headers, etc.) then you'll need
to adjust the mixture screws before attempting to adjust the idle air bleed
valve again. Adjust the screws in 1/8 turn increments, both screws the same
amount and direction, then try the idle air bleed valve again. If the motor
is stock and you can't get 30 degrees, then something is most likely broken.
If the dwell is always 30 degrees exactly, and adjusting the idle air bleed
valve makes no difference, then the motor is not running in closed loop.
Run the motor at 1500 rpm for a few minutes. It should go closed loop. If
it doesn't, something is wrong.
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>Post from: richardm at pig.net (Richard)
>-------------------------------------
> O.K. 1988 LG4 with factory electronic feedback carb.
>
> Immediately above the mixture control solenoid is a screw-in piston
>thingy with a spring loaded plunger that rides against the primary metering
>rod hanger. It appears that this assembly serves as both a rich-stop
>adjustment for the M/C solenoid and as a "biasing" for the soleniod.
>Adjusting it downwards applies more downforce to the M/C assisting the
>computer in holding it down against spring pressure. This, it seems to me,
>should cause the computer to narrow its pulse widths in order to maintain
>the same mixture. Likewise, adjusting it upwards should decrease downforce
>on the M/C plunger and cause the computer to increase duty-cycle in order to
>keep the M/C at its proper position.
>
> The small piece of a 1987 Buick service manual that I have talks
>about using a dwell meter connected to the M/C connector to set idle
>mixture. It's done with the engine closed-loop and idling. The adjustment
>is performed by turning the idle-mixture screws at the base of the carb.
>Fine and good.
>
> What's the procedure for setting this plunger doo-dad (that used to
>be protected by a plug)? Despite the fact that it appears to only affect
>the main-metering section of the carb, turning it has a very profound effect
>on idle mixture as well for some reason. I feel that I need to set this
>thing to the right positon before I play with the idle-mixture screws...