Observe a Mercury/Mariner WME 78 carburetor being disassembled cleaned, rebuilt, and re-assembled.
The “78” is the carburetor size and the “1” means it is the top carburetor. You will need to know the size to verify correct parts when ordering.
This is the fuel bowl drain plug and it is also used to access the main fuel jet. The jet can be changed with the carburetor installed but would be rather difficult.
This is the idle mixture screw, it is the only exterior adjustment on the carburetor, and only adjusts idle air/fuel mixture.
This is what gasoline does over time, the nasty green deposits plug your jets, fuel, and air passages, and will make you engine run lean as the jet passage will have a smaller open area for fuel to flow.
This is why the fuel should be drained, especially if the engine will sit for more than a year without being run.
These are the fuel inlet needles right after removal; you can see how the tip is extended and crooked. They in conjunction with the seat and float keep the fuel level constant in the fuel bowl of each carburetor. These must have been aftermarket needles as the fuel has had a molecular reaction with the rubber. This is a major problem, and will lead to inconsistent fuel ratios to the cylinders. OEM Mercury needles are made of all steel.
New gasket kits and needles were purchased and will be installed in the three carburetors for this 90 HP Mercury outboard.
Carburetor assembly will begin next; there will be some links at the end of the video, to find items like float settings, idle mixture screw initial settings, etc.
Click the link below to go to the Mercury Marine website, then click “Launch Parts Catalog”, look for your specific outboard, stern drive etc, until you find the Mercury part number you are looking for.