When bike has been sitting for a long period, this ^ can happen. These slow jets are prone to become partially clogged. The orifices are so small that fuel tends to hang in there. Lighter fractions of the fuel will evaporate leaving the other stuff to remain. Once cleaned, I recommend to run your bike (for at least one tank) with a fuel additive that helps to (keep) clean the fuel system.
I can service my slow jets blindfolded without removing the rack, but I can imagine for you at the first time, it can be a bit difficult.
However prior to removing the rack, I'd do this little test. Have the bike idle or near idle. Than turn in (and then out) an individual airscrew and listen if you can detect a change in rpm. Rpm should change. Do the same with the other carbs, one at the time. Where the rpm does not change, that carb's idle circuit is suspect. The change in rpm will be subtle, but can be noticed. Prior to this, take note of the initial position of the airscrew by counting whilst turning in till it stops (gently, do not force to avoid you damage its tip!), so you can later reposition the screw exactly where it was.
If, after you've done this, one or more carbs do not show a change in rpm, you could try this:
Drain the floatbowl by removing the drainscrew completely. Then remove the airscrew completely*, so you can pour some WD-40, carbcleaner or brakecleaner in that opening and pray it will - by gravity - finds it way through the passage of the slow jet down to the floatbowl. If it comes out of the bowl, you'll know there is still some opening in the jet. There is even a little chance the cleaner will dissolve the blockage. Give it time. If there's still an opening, fuel with an additive may further take care of the problem.
* Note that in the orifice of the airscrew, there's a little spring which does not necessarily have to be removed. Just pay attention, it doesn't get lost.
