My '98 GS500E I recently bought has been running a bit rough on the highway at speed. It exhibits the classis lean surge I've read so much about. It only has 1800 miles on it. I had taken the carbs apart and cleaned them with no improvement. I even shimmed the needle with one #4 washer. It starts easily. I had the pilot air screw at 2.5 turns out. Today I took the carbs out again to see if I could find any other issues. After I took the pilot screws out I discovered there were no springs or washers behind them! The previous owner has taken the plugs out and must have disassembled the carbs and forgot to put the missing parts back in. Now I'm assumming because I bottomed the screw out without the spring and washer in there and backed it out 2.5 turns I'm running WAY lean when on the pilot! I can't believe the screws didn't back out on there own. I guess it's time to order some parts.....

The purpose of the spring is to prevent the needle setting from wandering due to vibration.

It's omission will not prevent proper adjustment of the screw's needle.

Did cleaning the carbs and installing the washers fix your mid and top end problem?

Mmmmm close, but not quite ...

There is an O ring in the bottom of that whole spring and washer. The spring primarily puts enough preload on that O ring to keep it squished in place and not let in air.
The spring also of course keeps the screw from comming unscrewed and falling off.
You can say that you will be able to compensate for the air and fiddle with it and get it sorted ... but, if the screw falls off, you're SOL.

Send $10 and say $2 mailing to the buddha and a set of air screw spring+washer+O rings will appear in your mailbox magically.
Cool.
Buddha.