How to Repair Small Engines: Cleaning the Carburetor

Step 1: Diagnose the problem

Photo 1: Test for gas at the carb

Clamp off the fuel line. Then compress the spring clamp and slide it backward on the fuel line. Pull the tubing off the carburetor nipple and catch the gas in a small bowl.

Don’t google “small engine repair near me” next time you need an engine repair and instead learn how to do it yourself. 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. Look at your lawn mower carburetor.

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

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

Photo 2: The carb comes off easily

Use a socket or nut driver to remove the two bolts that hold the carburetor to the engine. Then unhook the throttle cable from the carburetor linkage.

How to Repair Small Engines: Cleaning the Carburetor

Photo 3: Corrosion’s a deal breaker

Junk the carburetor if the inside is corroded. Even after cleaning, the corrosion will clog the jets and tiny orifices and restrict the flow of gas.

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,”).

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

How to Find Carburetor Parts and Prices

Whether you buy parts from a local small engine repair shop or online, you may need all this information:

Machine brand (Toro, Snapper, Honda, etc.),model and serial number.
Engine brand and serial number (Tecumseh, Briggs & Stratton, Honda, etc.). The engine model and serial number are usually located on a plate above the spark plug.
You may also need numbers from the old carburetor itself (usually stamped onto the carb body or its mounting flange).

I prefer buying locally, but if you’re an Internet shopper, try these sources: smallenginepartswarehouse.com or psep.biz.

Step 3: Rebuild the carburetor

Photo 4: Dissect the carb on your workbench

Start the disassembly from the bottom (bowl, float, needle, seat, etc.) and keep all the parts together. Shoot digital photos for help during reassembly.

Photo 5: Dunk it and walk away

Wire all the larger parts together and drop them into a bucket of carburetor cleaner. Wrap the small parts in aluminum screen or use a fine-mesh basket.

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.