How do I clean the carburetor if old gas has clogged it?
Cleaning your small engine’s carburetor isn’t terribly daunting, but I recommend that you have the correct service manual for your engine and a carburetor rebuild kit on hand before tackling it. It’s a good idea to start this project without significant pressure to get your machine running that same morning, as it may take a bit of time.
You will need plenty of clean, lint-free rags; some carburetor cleaner (visit your local auto parts store; I prefer aerosol carb cleaner); glass, glazed-ceramic, or metal container(s) (or plastic that you know won’t be dissolved by the cleaner); eye protection; and chemically stable gloves. You will also want to read the safety information provided with the carburetor cleaner carefully, and work in a well ventilated area. Carb cleaner usually contains strong organic solvents that are flammable and poisonous, so be smart. Those solvents might also strip paint, eat the plastic lenses of your new spectacles and strip your skin of any lipid available on the surface — be careful!
Follow your engine manual’s instructions for removing and disassembling the carburetor — watch that you don’t lose any springs, screws or other small bits. Clean each piece carefully taking advantage of the strong solvent characteristics of the cleaner. Take special care with the little orifices you see in the carburetor body and in some of the valves. Avoid the temptation to ream the orifices with anything other than compressed air or aerosol cleaner. Those tiny openings are all related to gasoline and air flow and have everything to do with making the engine run efficiently and effectively. Once the pieces are clean, lay them on clean rags to dry, or carefully blow them out with compressed air.
Using your manual as a guide, reassemble the carburetor (install any new components included in the rebuild kit such as gaskets, needle valve, etc.). Reinstall the carburetor to the engine, and adjust it according to the engine manufacturer’s instructions. This last step usually requires an initial setting with the engine cold and a final setting once it has warmed up.
Some folks use a degreasing all-purpose cleaner called Simple Green to clean up their carburetors. Although Simple Green is one of my favorites for getting grease and oil out of my shirts and jeans, I doubt it would work well for removing the varnish deposits associated with old gasoline without heat. (I wonder what my wife Kate would say to the gassy, oily scent of boiled carburetor in her favorite Le Creuset pot?) If you go this route, please be sure the carb parts are free of gasoline residue before getting them anywhere near a stove burner.
— Oscar H. Will III, editor, GRIT magazine