Funny, most old Merc's I've run have had the same issue. Merc's way of lubricating the transom! You can see on the later models how they 'fixed' the problem by putting a plastic tray in the bottom front of the cowling to catch the fuel, then when you tilted the motor back down a rubber hose would direct the fuel overboard:^
Very environmentally conscientious:}
Anyway, if you don't have fuel spilling out of your carbs when you pump the primer bulb normally, and there's no fuel spilling out the carbs when the motor's tilted down and running, not much value in adjusting the float level as it's not going to correct the design issue.
Thanks for the replies,,,,,, sounds like I dont have a problem then, just a messy engine. BTW, mine does have the tray on it thats suppose to catch the fuel.
