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A dysfunctional carburetor makes boating no fun. When your outboard carburetor is funky, with aging, cracked gaskets and poor fuel flow that's affecting the performance of your Mercury 115, it's time to pick up a carburetor rebuild kit, break out the toolbox, pour some carburetor cleaner in a pan and rebuild the carburetor. You'll take it apart, clean it up, replace the the carburetor's damaged parts with what's in the kit, put the carburetor back together and people will stand in awe of your ability.
Items you will need
2 clean dry pans
Carburetor rebuild kit
Place a clean, empty pan on your workbench. You will disassemble the carburetor over and in this pan to prevent fuel spills that result as you tear the carburetor down and drain the float bowl into the pan. Set a second pan alongside the first and fill it halfway with carburetor cleaner.
Remove the mixing chamber and the gasket from the top of the carburetor body by removing the two screws holding them in place, with a screwdriver. Remove the float bowl plug-main jet retainer, remove the gasket and remove the main jet, so that you can insert a screwdriver into the opening and remove the main jet from the side of the center turret. Drain the fuel present in the float bowl into the pan you're working over.
Invert the carburetor so you can remove the four float bowl retaining screws and lift the fuel bowl away from the carburetor body. Remove and discard the float bowl gasket and remove the nozzle stem gasket from the center of the fuel bowl.
Support the float and, at the same time, push the float hinge pin free of the mounting posts. Lift the float and the attached inlet needle from the needle seat. Detach the inlet needle from the float.
Soak the metal parts of the carburetor in the pan of carburetor cleaner as you remove them from the carburetor. Discard any gaskets removed or disturbed during the process of dismantling the carburetor. Allow the parts to air-dry before continuing. Replace any parts that are damaged or worn from the parts in the carburetor rebuild kit.
Hook the inlet needle spring over the float tab and lower the needle into its seat with the float hinge between the mounting posts. Slide the float hinge pin through the posts to secure the float. Center the pin between the posts. Place the stem gasket over the center turret.
Hold the carburetor body in the inverted position -- the same position it has been in since the start of the assembling procedures -- with the float resting on the inlet needle. Measure the distance between the float bowl gasket surface with no gasket in place and a point on the float directly opposite the hinge using a machinist's ruler. The measurement point is the lowest on the horizontal surface and the distance should be 9/16 inch.
Remove the float hinge pin to free the float if the float measurement isn't correct. Make the float height adjustment by bending the tab on which the inlet needle hangs. Repeat the adjustments until you get the correct distance between the float bowl gasket surface and the lowest edge of the float.
Install the main jet into the center turret of the fuel bowl. Tighten the jet securely. Install the gasket and main jet plug in the exterior wall of the float bowl and tighten the plug securely. Keep the carburetor inverted and position a new gasket onto the body. Set the fuel bowl in position and secure it in place with the same four screws you removed initially. Tighten the screws snugly and position a new gasket over the mixing chamber. Reinstall the carburetor cover and the job is complete.
- "Mercury Marine Outboard Repair Manual 65-300 HP 1992-2001"; Seloc Marine; 2007
Will Charpentier is a writer who specializes in boating and maritime subjects. A retired ship captain, Charpentier holds a doctorate in applied ocean science and engineering. He is also a certified marine technician and the author of a popular text on writing local history.