On Webers, which is what we're talking about here(not Dells), the idle volume(mixture?) screw O-ring likes to stick to the carb. The O-ring doesn't go into the threaded area like Dells do, it just sticks to the flat that it tightens on. Remember, get the screw, spring, curved washer and O-ring.
On the idle jets, those JayCee jet holders can really change the way your day goes on a Speedster. You can use an allen key to spin them out, without getting interference from the carb top/fuel inlet, like you do when using a flat-blade screwdriver.
When you take the idle jet holder out along with the idle jet, make sure you get the O-ring too, that likes to stick in the holder well. VERY IMPORTANT not to lose this. This O-ring is best kept track of by rolling it down towards the head of the jet holder over all the threads.
Robert, that is the correct screw to remove along with the idle jet to clean the entire idle circuit.
I never had a problem like others seem to with plugging jets. I drove my car often and used Stabil to mitigate the white goo that forms in float bowls. Once the air is synched and linkage is set there is no reason to remove the air cleaners. IMHO this is where a lot of problems occur as there are openings on the carb top for the idle air intake and float well venting: great places for dirt to fall into. Every time you pull an air cleaner top you are asking for a clogged jet.
Good fuel filtration, clean carbs, and leaving the air filters alone are all you need for problem-free Webers.
Turning the carbs around by using CB Performance Space Saver manifolds is a GREAT idea, but only if you're running a 911 shroud or possibly a DTM. The regular VW shroud is so close to the number 1 cylinder idle jet and mixture screw it is VERY difficult to remove either.