Date registered: Oct 2008
Vehicle: 1959 190, 1961 190SL, 1967 250SE 4Spd, 1968 220D 4spd
Mentioned: 1 Post(s)
Quoted: 5 Post(s)
A basic thing to check is that the two carbs draw air in equal amounts. A synchrometer will help with this, but you will likely need some kind of flange adapter to fit correctly. You can adjust the air volume via the idle control screw on each carburetor. Make sure to disconnect the linkage between the two when doing this.
If the carbs are drawing air equally, but idle is unstable, there's likely an air leak somewhere, which is compromising the air/fuel mixture. This can have several causes, but a carb rebuild could be required. Not too difficult with those carburetors.