Hi,
On the 274 carbs fitted to postwar machines there is no provision for altering the fuel level. Any wear that has taken place will raise the fuel level. Should this level become excessively high, fuel will seep out of the bleed hole in the slot in the body just above the cap nut that secures the choke block. Up to this point, any discrepancy in the mixture strength should be adjustable on the slow running screw. It is unlikely that the slight increase in fuel level will drastically affect the mixture in the higher throttle ranges. If the mixture strength is erratic, check that the float and it's needle are free to move in the float chamber body - there is a hole about 3mm dia in the bottom of the float chamber that can get clogged up with dirt, making the float stick in the chamber. Also, check that you have the correct cap nut and washers between the carb body and float chamber - Amal made 2 depths of cap nut!
Hope this helps,
Regards,
Eddie.