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Old 05-02-2013, 10:55 PM
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Originally Posted by mustang 671 View Post

am running 70s in the primary's not 72s but still pig rich

I presume once I change down a jet I will know if its better as the air mix screw will start to operate ?? or with the sec throttle blades open will that also not allow the air mix screw to not function ?
This is not a jet issue.. Non responsive idle mix screws is caused by the throttle being too far open or too far closed at idle.
And or the primary and sec throttles are uneven or out of place at idle.

Throttle open position at idle
BOTH primary and sec is critical. Get it right and the idle screws will miraculously work.


Lock out the spark advance so it is fixed and does not move with rpm. Set it at about 30-32deg ( casue you got no boost retard. Now remove and flip over both carbs and reset the PRIMARY an SECONDARY throttle T slot exposure at idle.
Set the al the same as a start point. aprox .020" T slot exposure.. reinstall the carbs.
Fire it up and let it warm up and reset the idle mix screws on both carbs for best idle.
If the idle speed is just too fast then close the secondaries on both carbs the same, BY A TINY AMOUNT.
IF THe IDLE SCREWS ARE NOT WORKIN have no effect THE THROTTLES (either the primary or the secondary or BOTH) are out of position.

Last edited by F-BIRD'88; 05-02-2013 at 11:02 PM.
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