Pull the carbs, check the jets and clean the pilots. This is what I did with my bike and ATV (both have Mikuni) and Poo uses Keihn but the principals are the same. You can use a this piece of thin wire to clear it out or a set of orifice bits (used in cleaning orifices in furnaces). I'd bet that your pilts jets are clogged as they are on the idle circuit.
A quick rundown:
Main Jet= 1/2 throttle to WOT
Needle jet= 1/4 to 1/2 throttle
pilot jet=idel to 1/4 throttle.