Will it do that when the engine is fully warmed up? What's the total engine run time when this happens, or will it happen regardless of engine run time?
Option 1: Idle speed is set too low - there will generally be an adjustment knob somewhere, either on the carb(s) itself or on a cable connected to the carb, if this is the case it will frequently be a plastic knob on the left side of the bike near the carb.
Option 2: Idle mixture is set too lean. Very common on older carbureted Hondas. The idle mixture screw will generally be recessed into a hole on the carb body on the bottom pointing straight up, just behind the rubber boot that connects the carb to the cylinder head. I don't know if that bike has one carb or two - if there are two, there will be a separate one for each. Turn this screw fully in until it seats gently and count the number of turns. Then turn it out but add half a turn more.
Option 3: Slow jet(s) are clogged. Common on a carbureted bike that has been improperly stored. Only fix is to take the carb(s) apart and clean the jets out.