Carb Sync Problem w/ $5 DIY tool

[LostND80s]

Hey guys, Im having some problems getting my carbs properly synced.  If anyone could shed some light, it would definitely be appreciated.

Here's whats going on:
I have 2000 GS500.  I did a solid carb cleaning about a month ago, o-rings and all.  Swapped out the fuel filter, did some other light maintenance, etc.  When I start it up now, it runs well, and idles good... however, when I take it for a ride, it seems to take a long time to come back down to idle after I rev it.  Also, when it's just sitting at idle (at a stop light), I see some/alot of white-ish smoke coming from the exhaust.  This scares me, so I figured I missed something after the carb cleaning.

I checked the compression w/ a guage, and Im seeing >140 on the left, and <150 on the right.  I assume this is OK.

I heard that a vacuum leak might be causing the problem, so I checked for leaks w/ starter fluid.  Sure enough, I got some funky behavior when spraying the connectors to the carb/engine... so I reseated them.

Along with this, I wanted to resync the carbs.  When I checked the spark plugs, I noticed that the left was black, while the right was white-ish... This seemed to indicate that they were running differently.  So, I built one of the $5 DIY Carb Sync tools, t-connectors, on/off valve, and all.  I used 1/4" tubing and connected it under the caps on top of each carb.  Filled it with 10W40 oil.  I set idle to 1750, and immediately noticed that it was out of sync.  Left side was about 50% higher than the right.

I started playing with the sync screw, and after a few turns CCW, the idle would jump up to 4k or so.   So, I'd turn down the idle screw and continue.  I kept going and going, and the oil would drop on the left, but only slightly compared to how much I was adjusting it.  Then it would rev up, and I would have to re-tune the idle screw.

Is this normal?  Is there another problem?  Please keep in mind that my ON/OFF valve of the carb sync tool is COMPLETELY OPEN... and Im still seeing far more vacuum on the left side (higher oil).

Any ideas?

Thanks,
-Jason