Re: carb flooding when engine off
You need to trouble shoot it to find out what is happening. If the enricher is the problem, no amount of cleaner gunk will help. If a needle valve is nicked, or a float sunk, no amount of cleaner gunk will help.
Mercury parts express is down, or else I could get an exact mechanical drawing of your engine. I can only speak in generalities.
First, be sure all pressure is removed from the fuel system as soon as it is shut down. Disconnect the fuel line from the engine. This will eliminate the possibility of fuel being forced into the engine from the tank because of a plugged vent.
If gas is running out now, it has to be either a serious fault or crack in the carburetor, or it is from a fuel enricher circuit. If the carb has a choke butterfly (on the input flange, not the engine side of the venturi) then it does not have an enricher. If it does not have a choke, look for small lines going to each carb, probably one from the bottom of the top carb, and lines from the top of the lower carb, or both carbs. They would all lead to an enricher solenoid. It could be stuck open, and would give you the symptoms described. The enricher valve allows the suction developed behind the closed or mostly closed throttle plates to pull fuel from the float bowl of the top carb into the intake manifold. A stuck valve probably would not bother much at higher speeds, as the vacuum is less then and the excess fuel would just be burned up.
If gas is not running out now, you have a combination problem of pressure from the tank and a stuck needle valve. The valve could be damaged, or the float could be sunk. Either way, it's time for a carb kit and maybe a needle and seat or float as needed. Another possibility is a damaged or missing internal float chamber gasket. Also trouble shoot the tank venting and be sure it is right.
If the floats and needles are working, you should be able to pump the primer bulb to a firm feeling with a moderate squeeze and not have any fuel flowing out anywhere. A white knuckle grip will overpower the needles and flood the carbs. That's normal.
I'm taking a shot in the dark without diagrams. Hope it helps
John
