Roxy: Not So Fast!!

Arrrghhh!!  Starting her up again today and she won't hold idle anymore!  I rode Golden Gate Park yesterday and she idled beautifully start to finish.  But now I'm getting the exact same exact symptoms as before.  I repeated my steps from Friday to clean out the slow jet and circuit, figuring maybe it just got clogged again (in which case I'd know I'd have to replace the filter).  But even after a cleaning, there was no change.

Again, I tried messing with the screws, but it was either a weak idle, or a racing one.  There never seemed to be anything in-between.

Troubleshooting brainstorm:

1. Maybe it was the long ride yesterday that actually just gunked up the circuit again, maybe more than just the WD40 spray could fix.  Maybe I should replace the filter, clean the circuit out yet again (I just realized I didn't spray out the air screw hole), then if she holds idle after several rides, I know it was gunk from the tank getting through the old filter.  I guess if I clean out the air screw hole (thereby repeating ALL the steps from Friday) and she at least holds idle for awhile, then that would prove that it's just getting gunked after a long ride.
2. I noticed the rubber gasket on the choke handle was ripping off.  If that creates an air leak, then there's my problem right there.  Wondering if I can temporarily seal it with vaseline just to test it.  But then again, I think it was ripping this whole time, so surely it was in bad shape even for yesterday's ride (in which case, it has no effect on idle).
3. Replace the kinked throttle valve spring.  It's possible the weak idle is just a bad setting of the screws.  Maybe when it races, that's the correct screw setting, and maybe it's the racing idle that should get fixed.  The racing idle could be a sticky slide.  But then again, she ran fine yesterday.
4. I prepped the original carb (labeled S90B) that I cleaned yesterday with new parts from the Keyster kit.  I can swap it out, but since I might need to cut the old fuel lines, I should be ready with new tubes and a fuel filter.  One difference is that the S90B has the fuel line on the opposite side of the carb body.  Just for reference, Viola's carb is labeled CS90C.
5. Finally, I'll just try pulling the current carb (labeled S90K1E05) and give that a thorough Pine Sol dip.
6. It may also not be the carb at all, but rather a faulty advance unit.  But given that the problem was intermittent, seems like it must be the carb?

Here's Roxy's original S90B carb cleaned, rebuilt, and ready to go.  I took the intake (the one I painted), gasket, and insulator Viola's carb.  From the Keyster kit, I used:

1. air screw
2. throttle screw
3. slow jet
4. main jet
5. bowl gasket

I also replaced the intake gasket (finally opened the gasket set), hoping it could be a simple air leak, but no luck there.