I just purchased this bike, when I bought it it had a smoking issue.  It is whitish smoke with a blue tint and smells like burning oil.  It does it hot or cold. 

Heres what I've got so far.

Bike starts fairly easy (nothing to compare it to however, but in my opnion starts up easy)
Left plug was badly fouled, replaced both.
Changed oil
Pulled and cleaned carbs
New Battery
Compression left 105 compression right 140
Wet compression left sky rocketed and same with right.  I don't remember the number now but both shot very high.

Valves
I guess I need to get a new feeler gauge the smallest mine goes is about .0324mm however it will not fit in left intake, or right exhaust or intake.  The left exhaust is between .152 and .178 (.152 will go and .178 wont).

Looking at those numbers can we assume that the valves are my issue and once fixed should stop my smoking , only other thing I can think of is piston and rings but compression didnt seem that low.  Bike runs well when running, it has a flat spot between 2-4k rpms but then it runs great.

Your valve numbers seem odd to me...... isn't the spec .03-.08 mm? I know that even .10mm is used as a high limit, but above .15mm seems pretty big. Definitely wouldn't hurt to get them all within spec.

If pouring oil into the left cylinder shot the compression test up, I would say it's the rings on that side. Give it a couple hundred miles.... the rings might bed in again and solve themselves.

And a flat spot might be your carbs too. Does your current jetting match with any intake / exhaust modifications?

+1  Agree with Rich on likely source of smoke and on giving it more time.

I set exhaust valves a little wider than the .10 mm mentioned, copied from recent post of mine:

..........the tighter of the 2 exhaust valves on my 97 GS running at the minimum Suzuki spec most of the time required constant shim changes and was down to a min 215 shim by 80k miles.  When the tighter one on my 02 GS started the same pattern at about 30k miles I increased the exhaust valve clearances to .003-.005" (.08-.13mm) and they stabilized after that requiring little more change than the intakes did.  Min shim in the 02 at 100k miles is a 245.  Suzuki's tight tolerances did not provide enough cooling seat time for exhaust valves.


My valve check record:

http://www.gs500.net/gallery/data/500/GSvalvelogs.jpg

Checked my compression recently at 100,500 miles on engine while troubleshooting another problem:

                  #1 cyl             #2 cyl
Cold             135 psi          135 psi
Hot              140 psi          140 psi                           
Oil added
to cylinder    200 psi          190 psi

You seem to know what you're doing so I hesitate to mention it but your 105 psi for the left cylinder is about what I got at first when I forgot to hold the throttle wide open while checking.   

Your flat spot at 2-4K on your 98 reminds me of my 97, it was flat below 4k and I never ran below that on the 97 for the 80k miles I put on it running completely stock all the way.  My current 02 will pull smoothly from 2-3k in top gear with the newer 3 circuit carbs and remains stock.
                 

chade i had almost those exact issues.

Valve adjustment and replacing both piston rings and cleaning out the insides really well

fixed it all