How To Clean Inboard Boat Carburetor

Author: Grid Michal
Sometimes when I talk to my customers about ethanol's effects on marine engine fuel systems, I see their eyes glaze over. It is to the benefit of my IRA that I still have customers who don't pay attention and who don't take time to care for the item that keeps them from paddling back home. Invariably, I have to clean carburetors of the junk that ethanol deposits — and with the specter of E15 hovering over us, things aren't going to get easier.

First, a carburetor is a carburetor. There are different types and quantities, but they all do the same thing: Fuel is pushed into a bowl by a fuel pump (unless the engine has an integral, gravity-feed tank), where it is pulled through a main jet, up either to idle circuitry or into the venturi, where a vacuum from a piston pulls it into the combustion chamber. Fuel is a coolant, so when its high-speed flow is restricted, the piston runs hot and melts, causing major damage and expense. When it's restricted at low speed, the engine won't idle properly. If you want to do the right thing and keep your carb(s) clean, read on.

Keep Your Carbs Clean Begin by disconnecting the fuel supply from the engine. Remove the air box from the front of the carburetor. Remove the hose that runs to the carburetor from the fuel pump. Most fittings are plastic, and the hose sticks. If trying to gingerly twist the hose free doesn't work, take a razor and cut the hose lengthwise where it attaches. It's cheaper to replace the hose than a carburetor or a fuel pump.

Take the carb to a clean work area with a grocery bag cut open to work on. Take the rest of the eggs from the egg carton in the refrigerator and put them somewhere they won't break. You're going to catch hell for what you did, so might as well try to get some credit, too.

DIY-02-2015-image-03 Remember, the odds are 100 percent against you that parts won't hit the floor. Clean the floor first. If a part hits the floor, it will roll under something. Preclude that eventuality however you can. Assemble your tools: safety glasses; Phillips, slot, very small, standard screwdrivers; needlenose pliers; fine brass wire; carb cleaner. If you have multiple carbs, use a separate container for each carb. Some manufacturers jet multiple carbs differently. Time to start operating.

Find the idle mix screw. Turn it clockwise until it lightly bottoms, and count the number of turns in. Write it down where you can refer to it later. Remove the screw and spring and put them in one of the egg carton cups. DIY-02-2015-image-05 Remove the bowl drain screw and put it in another egg cup. Remove the screws attaching the bowl to the body; put 'em in a carton cup. Remove the pin holding the float. Some pins are unidirectional. If it doesn't move easily, look for roughness at one end of the pin and remove the pin from the rough end. Remove the float and needle. Remove the main jet and the idle jet if it's behind a plug in the main orifice. Put them carefully into an egg compartment. If the carburetor is Japanese, it probably has an external idle air screw (in addition to the idle mix screw) that looks like a screw but isn't. Being plugged is often the reason a Japanese engine won't idle. Remove screw that isn't, put it in an egg cup. If the main emulsion tube is removable, remove it. If you have a Honda carb, remove the main emulsion tube and the idle tube. You'll want to buy a new idle tube from your dealer.

In a perfect world, everybody would have a sonic jewelry cleaner so he could clean his wife's diamonds and his engine parts. The world ain't perfect, so we compromise. Put your safety glasses on. Start with the bowl. If there's any crud in there, use a Dremel tool with a wire brush to assist the carb cleaner, and then use a Brillo pad. Spray the bowl clean with cleaner again and ensure the drain screw hole is clear.

Move to the jets. DIY-02-2015-image-04 Run wire through the main jet and spray the orifice to ensure spray goes all the way through. Ditto for the low-speed jet. The Japanese air "screw" doesn't have a hole that goes all the way through. If you can spray in the small end and spray comes out the horizontal orifices, it's clean.

All brass parts have to be spotless. Again, Brillo works well. Clean the float needle with the Brillo pad. Use a tiny ignition screwdriver and a paper towel soaked with carb cleaner to clean the needle's seat. Spray through the idle circuit passages. Clean the outside of the carb body. Make sure everything's dry, then start reassembly. Note: Do not cross-thread or be a he-man with threaded parts. Be gentle.

Reinstall the idle screw and its spring, lightly bottoming it, then bringing it back out the number of turns you recorded. Reinstall the low-speed jet. Reinstall the emulsion tube the proper direction. Follow that with the main jet. Run a bead of nail polish around where the emulsion tube enters the venture. Reinstall the needle and float, ensuring the float is level when you hold the carb body upside down. If it's not level, adjust it so it is. Install the carb bowl (aka float chamber). Reinstall the drain screw. Reinstall the carburetor on the engine. Put a film of oil on the fuel pump outlet and the carb inlet, so the new hose slides on easily. Reattach the external fuel source, squeeze the primer and see if the carb is leak-proof. BW