Let's try this
NOTE: You have to set the fast idle first. I tried to attach some illustrations from the manual I took this stuff from (don't know if it worked). It sounds to me that the screw you were adjusting is the holding screw for the choke cap. I could be wrong. The following is straight out of the manual. I suggest you get one, the info I quote here is from the library.....Good Luck and Merry X-Mas
Set throttle on fast idle cam top step.
Note index position of choke bi-metallic cap. Loosen retaining screws and rotate cap 90°in the rich (closing) direction.
Activate pulldown motor by manually forcing pulldown control diaphragm link in the direction of applied vacuum or by applying vacuum to external vacuum tube.
Measure vertical hard gauge clearance between choke plate and center of carburetor air horn wall nearest fuel bowl.
Pulldown setting should be within specifications for minimum choke plate opening.
If choke plate pulldown is found to be out of specification, reset by adjusting diaphragm stop on end of choke pulldown diaphragm.
If pulldown is reset, cam clearance should be checked and reset if required.
After pulldown check is completed, reset choke bi-metallic cap to recommended index position as specified in the Carburetor Specifications Chart. Check and reset fast idle speed to specifications if necessary.
'88 STX Super Cab 4x4
2.9 5spd 180,000 miles
Crappy Paint, Worn Parts,
Fix'em as they Break
when Nowhere is Now Here