How to Repair Small Engines: Cleaning the Carburetor

Step 1: Diagnose the problem

If you can't get a small engine started, or it takes too many pulls to get it going, or it runs poorly, ask yourself this: Did it sit for a long time with gas in it? Like over the summer or winter? If so, your problem is most likely a corroded or gummed-up carburetor. Small-engine repair shops earn about 50 percent of their revenue by cleaning or replacing carburetors that are sidelined by old gas.

Before you rip into the sucker, take a minute to confirm that the carburetor's the problem. I'll show you how to do that, as well as how to rebuild it or replace it. Either way, you'll save about an hour of shop labor (about $70). You can complete the project in a single morning, including the time scouting for parts.

I'll assume the fuel valve is on, there's gas in the tank and you've already checked the condition of the spark plug. Start by shooting a one-second burst of aerosol lubricant or carburetor cleaner down the throat of the carburetor. Then yank the cord. If the engine runs (even just sputters) and dies, you'll know you have a fuel problem. If there's no life after a few tries, it's something more serious and you'll have to haul the engine to your garage for some detective work. If it fired, remove the fuel line at the carb and check for gas (Photo 1). It should leak out of both the fuel line and the carburetor. If it doesn't, you've got a plugged fuel line or fuel filter.

Step 2: Remove the carburetor

Next, remove the carburetor from the engine (Photo 2). Place it in a container (to catch the gas) and open the carburetor bowl to check for corrosion (Photo 3). If it's corroded, it's toast—buy a new one.

If there's no corrosion, you can choose to rebuild it rather than replace it. But that doesn't automatically mean you should—rebuilding isn't always cheaper, and it might not even do the trick. In fact, sometimes you can buy a new carburetor for less than (or pretty darn close to) the cost of the rebuilding kit plus the cost of the chemicals (see “How to Find Carburetor Parts and Prices,”).

I always just replace bad carburetors, rather than rebuild them.

Step 3: Rebuild the carburetor

If you're game, spread out some shop towels and disassemble it (Photo 4). Match the new gaskets and O-rings in the kit to the old ones. Then set aside any extra parts (rebuilding kits often include parts for several models, so you might not use all of them). Next, dunk the parts in carburetor cleaner (Buy a gallon at any auto parts store) and let them soak for an hour (Photo 5). You can try using spray carb cleaner instead of the high-priced stuff, but it's a gamble (just be prepared to rebuild it again). Then rinse all the parts with water and blow them dry with compressed air. Install the new carb parts and mount it on the engine. Follow the instructions in the kit for adjusting the idle speed and mixture (or ask the parts supplier for advice). Then fire up your engine and listen to it purr.