I know it's an old thread but i chanced upon it..thought i'll make it clear for anyone reading this in future.
Quote:
Originally Posted by black12rr  Turning it right used to be rich and turning it left used to lean out , or am I confused  . |
The carb pictured above is a Mikuni BS carb, and the screw mentioned in the article is a volume control screw.
With volume control screw you tighten it for a lean mixture and loosen it for a rich mixture. This is because it controls fuel and not air.
The Mikuni VM series carbs have air control screw, tighten it for a rich mixture and loosen it for a lean mixture. This is because it controls the air entering the pilot circuit, more air = lean, less air = rich.
How to make sure if a screw is a volume control or an air control?
If the screw is near the engine, as in the picture, it's a volume control screw.
If the screw is near the air filter, like in a VM28, it's a air control screw.