the true centre point of adjustment is found by turnig the screw 20 turns in one direction then 10 turn in the opposite direction.
there is no stop at either end of the screws range so this is the only way to find its true centre.
anti clockwise richens the mixture, clockwise leans it off from there.
If the co pot still doesn't seem to work test it with an ohmmeter between either of the outer pins and the centre pin- it should read between roughly 448 and 5993 ohms- anything much more or less and the co pot is deffo not oworking right.
hope that helps fella