When you turn your throttle and look at your carbs on the right side of the bike, you see the throttle lever moving there. The position of minimum throttle is set by a screw with a spring on it, that's the idle screw. Turn it up a bit so you have a little bit more throttle as a base level, your idle revs should be slightly higher then. That usually helps against problems like bogging down and stalling while idling. If it doesn't fix anything, just put it back the way it was and look for problems elsewhere. My guess is that since there is some fluctuation in your revs, your bike is maybe running a bit lean. If you take a pic of your spark plugs we can see if that's the case (here's how to read spark plugs)