Recently worked on a friend's refreshed 4A-GE sporting a pair of Mikuni 44PHH carbs. While dialing her in, in between the test jaunts she started developing an ever increasing sticking throttle. Pretty soon, the idle had jumped from 950 to 2000+. The entire carb-to-intake assembly was sitting on my bench while the engine/car were being prepped and no binding/galling was ever observed. Still, we went through a litany of the usual suspects:
over-tightened throttle shaft nuts
linkage arms catching on hoses, etc...
linkage jam nuts coming loose and adjustment shaft(s) extending on one/both of the linkages
throttle plates open too much via the idle-speed screws (shouldn't be no more than 1 full turn in from first contact)
catching on phenolic spacers/intake port
slight twisting to carb body due to uneven mounting surface(s)
After eliminating the possible causes mentioned, we loosened the linkage arms and opened the throttles independently. It was only happening with carb 1 - removed it along with the linkage and linkage arm still connected. That's when I noticed that the linkage arm was keeping that "hockey stick" position while I held up the linkage and even as it dangled below the carb when I let go.
I happened to have spare ball studs and moved the linkage to the new ball stud - same thing. "Maybe it's the Redline linkage?" I had a brand new identical one NIB - same thing, again. I reinstalled the original ball stud next to the new one and swapped the linkages between the 2 and tested both ends - same exact issue.
So I just put the ball stud in my drill press and took 220 grit sand paper to it:
and test fitted the linkage every so often until I had removed enough material to where the linkage freely drooped down on its own weight when I let go:
Cleaned everything up, re-attached the carb and linkages, confirmed idle-speed settings and synched up both Miks and voila! No more sticky throttle. It should be noted that the linkages and ball studs are both Redline products and sometimes there are inconsistencies within the same product line during manufacturing. Don't be surprised if there are larger disparities between different manufacturers when mixing and matching components intended to work hand in hand to accomplish your intended task.
Look at it as an invitation for YOU to be more than just another cog in the assembly line mindlessly snapping things together. Dig it?