Idle Adjust screw (2) is fuel mixture adjustment screw. 
Turning counterclockwise will result in a richer mixture, clockwise for leaner mixture. 

Basic adjustment: 
Open appr. 1½ to 1¾ turns from full closed position.

Cylinder #1 (rear Cylinder):

Main jet: 126
Jet needle: y - 21
CO-value: 4%

Cylinder #2 (front Cylinder:

Main jet: 124
Jet needle: y - 20
CO-value: 4%

Pilot jet for both is: Nr.: 43

Note: CO-value is taken within the exhaust's (6 mm allenscrew).
 

IMPORTANT NOTICE: 
Drain fuel from both carburetors when putting away the bike for a longer period of time to avoid detoriation of the fuel and grudge forming within the carbs. 

If your bike has a hard time when cold, it's most probably due to grime within the choke-valves in the float cover. To see whether they are clear, check with a slanted flashlight beam. 

If you encounter tears in the diaphragms of the vacuum piston assembly (which can only be replaced in one piece acc. to Yamaha = DM 250 (apiece)!) lead to bad throttle response and engine run up.