Greg;
High idle after a speed-run suggests linkages are not returning to the idle location...I'd assure all linkages and return springs are well lubed and free to move unimpeded...besides being properly adjusted...!
DX Metering Needle is OK, just be certain it is installed correctly, with shoulder flush with Daspot bottom surface.
Source:
https://www.sw-em.com/SU%20Carb%20Service.htm
OK on checking for False Air leaks, but if there were any, you'd likely not be able to bring down idle under any condition...
If it takes four full turns down on the Jet as a baseline, something is very different (wrong?) from the typical nominal adjustment! ...I agree with RiM to check and assure fuel level...also check to assure Jet supply line is not clogged or somehow occluded or fitting at bottom of Fuel Bowl has an issue (such as squished, partially restricting flow)...also verify there is no excessive silt/rust particles in the Fuel Bowl Sumps or even in the Jet Supply Line which is limiting fuel flow (this had me stumped once also...remedied by blasting carb cleaner with a snoozle, back through the Jet!)...See alsu:
https://www.sw-em.com/su_carbs.htm#I...et_Replacement
As another thought, assure you have the correct Dashpot Return Spring...it should be Red (if color is ascertainable) otherwise someone can measure and post springwire gauge and freestanding length...SUs are highly configurable and different springs were available for service in different displacement engines, so you must have the correct one installed for our 1.8/2.0L engines.
"carbs exhale a fuel mist when I blip the throttle"...this is called "Reversion"...it is a common effect, (only) during sudden Throttle opening on our SUs...well-known (especially also on DCOE sidedraught Webers! See:
https://www.youtube.com/watch?v=Vw1ihxlCIzI ), but nothing to worry about, unless excessive (or you ignite that flammable fuel/air mixture!!!), indicating a Cam/Valve timing issue...carb adjustment is done with Air Filters removed for better access and so you can view relative positions of Dashpots of both carbs...they should be fairly similar in position at all operating conditions (idle, blip, etc), but I always say: Don't make yourself crazy try to get them absolutely identical! Because you will surely make yourself crazy
before you get them identical!
I don't so much think that a balancing tool is an absolutely necessary thing when the comparative heights of the Dashpots are right there in plain view when Filters are not in place...in fact, that is what the "bent wire" indicators are based on, except these allow Air Filters to be left in-place...but to use them, Dashpot Dampers are
not in place, so Dashpot action when blipping Throttle cannot be checked as there is no damping and enrichment.
I love Tri-Flow where a light lube is called for (see:
https://www.sw-em.com/Product%20Reviews.htm#Tri_Flow )...sure you could use it on your SUs and associate linkages, and it will work well, but given elevated engine compartment temps, which will cook it away in not so long a time, so it will need reapplication, I'd prefer a light grease, or even a graphite filled grease, which stick around a lot longer, not to mention the graphite particulates...
...but those 24 flats are still bothersome to me...that would be the first priority to sort for me...
Good Hunting