Since both sides are running rich, it would be a really rare thing if both carbs had the same problem, so they should be moved to the bottom of the list of things to check unless the problem started after some work was done on them.
Suddenly rich mixture can usually be caused by 4 things. Reduced air flow or increased fuel flow changing the mixture or weak/late spark or loss of compression causing the mixture to burn poorly.
If the spark or compression were off, you would know right away because there would be a serious loss of power.
Air flow is the easiest to check. Make sure the filter is flowing OK by, as has been suggested, remove it, clean the plug, and see if the problem goes away.
If the problem is still there, take a look at the seat pan. If it has somehow gotten cracked, it could sag enough to block the airbox inlet.
Feel around inside the airbox to make sure nothing is blocking it. While you're there, see if your bike has the rubber tubes in the passages to the carb's. (some have them, some don't) If they are there, squeeze the ends to disengage them and pull them out. Just leave them out, you will gain a couple HP without them. If they've been contaminate with CARB (Calif Air Resources Board) mandated gas, they may have softened enough to collapse when air is being pulled through.
OK, having eliminated air flow problems, that leaves the possibility that fuel flow is increased.
I see you live in CA so, unless you bought the bike elsewhere and then moved there, it came with the vapor recovery system. If the tank was filled vary full, especially in the morning when the gas is cool and more dense, then it sat where it would warm up before any significant amount of fuel was used, the gas may have expanded enough to overflow into the vapor recovery system and filled the canister. If this is the case, exess fuel will cime up the purge lines and richen the mixture. If you are careful to fill the tank no more than to the point where the gas touches the lowest part of the ring at the bottom of the filler neck when the bike is on the sidestand the problem will soon go away.
According to the manual, at least some of these bikes are equipped with a filler cap that has a 1 way vent valve that lets air into the tank but not out. The idea is to force the evaporated fuel through the lower vent hose into the vapor recovery system. If you have the vented cap and the lower vent hose has been pinched or the vapor recovery system has been clogged, it is possible that the tank is building up pressure and forcing fuel past the float valves. With about 1/2 tank of gas, remove and replace the cap in the morning to equalize the tank pressure, then let the bike sit in the sun for a while. When the tank is warm to the touch, carefully loosen the cap and listen for a hiss indicating pressure escaping.
There is one thing that can affect both carbs. Make sure the "choke" is shutting completely off when you push in on the knob.
