Mercury offers two-stroke outboard motors with carburettor-type intakes. Carburettor banks hold two carburettor bores that draw from a shared fuel bowl, and each cylinder gets its own carburettor. The gas/oil mix that two-strokes run on can evaporate during long periods of disuse. The oil collects in the bottom of the fuel bowl and in any fuel jets in the fuel bowl as the gasoline evaporates. The remaining oil turns into a gel that does not dissolve in fresh gas, and that must be removed mechanically and with carburettor cleaner. Once the carburettors are removed from the engine, disassemble them for cleaning.
Remove the large brass screw from the side of the fuel bowl on each carburettor bank with a flat screwdriver and drain the fuel from the carburettor. Use a clean shop rag to absorb the fuel as it drains from each carburettor bowl. Use caution when removing this screw as the steel screwdriver can easily deform and destroy the screw head.
Remove the four fuel bowl screws with a #2 Phillips screwdriver. Lift the bowl up and off the carburettor body.
Remove the main jet and pilot jet from the bowl with a small screwdriver or jet driver. Use caution to avoid damaging the soft, brass jets and possibly restricting the precisely metered orifice.
Clean the jets out with a jet pick or torch cleaning tool. Remove as much of the oil gel as possible with the pick, then wash the jets in carburettor cleaner to remove any remaining residue.
Dig out as much of the oil gel in the fuel bowl as possible. Rinse the fuel bowl well with carburettor cleaner until all traces of the gel are removed.
Put on safety glasses or goggles. Blow through the fuel passages in the bowl with compressed air and an air nozzle to remove any remaining gel in the system. Shoot carburettor cleaner through the passages and blow them out again with the air to ensure that they are clean.
Spray carburettor cleaner through the upper air-intake jets on the carburettor body. Observe the air ports in the carburettor barrel to ensure that the carburettor cleaner is coming out of the port, indicating a clear air passage.
Shoot carburettor cleaner and compressed air through the main-fuel and pilot-fuel pickup tubes in the carburettor body. Observe the fuel ports in the barrel and ensure that the cleaner comes through the port.
Reinstall each of the jets, and tighten them securely with a small screwdriver or a jet driver. Blow all remaining traces of carburettor cleaner, gel and/or debris from the carburettor body and fuel bowl.
Place the fuel bowls in position on the carburettor body. Install the four bowl screws and tighten them securely with a #2 Phillips screwdriver.
Install and tighten the brass drain screws in the fuel bowls securely with a flat screwdriver.