According to the Mikuni VM Carburetor Super Tuning Manual I have, the float adjustment for the height of the rib for the float arm in a VM 38 is between 0.66 and 0.74 inches (or 17 to 19 mm). That doesn't appear to mean much. The illustration looks like you adjust for a level (or straight out) float arm with the carb upside down. Hope that helps.
1998 Arctic Cat Cougar
1999 Arctic Cat Z 440
1995 Ski Doo Formula STX LT
Usually with Mikuni carbs you should set the float height parallel with carb body holding it upside down, just like ACMan said. Be very careful if you are going to take the float off the carb, because the small casted towers where the float holding pin goes is very easily broken.
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