What You Need to Know Before You Start

A carburetor mixes air and fuel in the right proportion so your engine can run. When it fails—usually because internal passages clog with old fuel residue—the engine won't start, runs rough, or stalls under load. Replacing it is often simpler than rebuilding one, and the job takes two to four hours on most small engines like lawn mowers, generators, and chainsaws.

Before you buy a replacement, confirm your engine's exact model and year. The carburetor for a 2015 Briggs & Stratton 5.5 hp is not the same as one for a 2018 model, even if they look identical. Check the engine's metal tag or your equipment's manual for the model number, then order the exact replacement part. Aftermarket carburetors are cheaper but may not fit as precisely; OEM (original equipment manufacturer) parts cost more but bolt on without modification.

This job requires basic hand tools—a socket set, screwdrivers, pliers, and a clean workspace. You'll also need a small container to hold fasteners so you don't lose them, and a rag to wipe away old fuel and dirt. If you're uncomfortable working with fuel or your engine is still under warranty, a small-engine repair shop can do this work for $75 to $150 in labor.

Key Takeaways

  • Order the exact OEM carburetor for your engine model and year before you start, because aftermarket versions may not fit without modification.
  • Drain the fuel tank completely and let the engine cool for at least 30 minutes before you disconnect the old carburetor.
  • Take a photo of the fuel line, throttle cable, and choke cable connections before you remove them, so you can reconnect them in the same way.
  • The new carburetor usually comes with a gasket and mounting hardware; do not reuse the old gasket, as it will leak.
  • After installation, the engine may need a few pulls to draw fuel up through the new carburetor before it starts.

Gather Your Tools and Prepare the Engine

Lay out your socket set, screwdrivers (both Phillips and flat-head), pliers, and a clean rag on a flat work surface. You'll also need a small drain pan or bucket for any fuel that spills, and a container—a small jar or cup works—to hold bolts and screws as you remove them. Label the container or take a photo of each fastener's location so you remember where it goes.

Turn off the engine and let it cool for at least 30 minutes. Fuel and hot metal are a dangerous combination. While it cools, locate the fuel shutoff valve (if your engine has one) and turn it to the off position. If there's no shutoff valve, you'll need to drain the tank. Tip the equipment carefully into the drain pan or siphon the fuel out using a hand pump—never use your mouth to start a siphon. Dispose of old fuel at a hazardous waste facility or gas station; do not pour it down a drain.

Disconnect the Fuel Lines and Control Cables

Before you touch anything, take a clear photo of the carburetor and the lines connected to it. This photo is your map for reassembly. You'll see at least three connections: the fuel inlet line (usually rubber tubing from the tank), the throttle cable (a thin metal cable with a spring), and often a choke cable (another thin cable, sometimes spring-loaded).

Start with the fuel line. Loosen the hose clamp at the carburetor inlet using a screwdriver or socket, then gently pull the line free. A small amount of fuel may drip; that's normal. Pinch the fuel line with a clothespin or clamp to prevent siphoning if the tank is still partially full.

Next, disconnect the throttle cable. This cable is usually held to the carburetor by a small bolt or a clip. Loosen the bolt or unclip the cable, then carefully pull it free. Do the same for the choke cable if your engine has one. These cables are under spring tension, so work slowly and keep your fingers clear of pinch points.

Remove the Old Carburetor

The carburetor bolts to the engine's intake manifold using two to four bolts, usually 5/16-inch or 3/8-inch. Use the correct socket size—forcing the wrong size will strip the bolt head. Loosen each bolt a quarter turn, then remove them one at a time and place them in your labeled container. Do not remove all bolts at once; loosen them gradually so the carburetor doesn't fall.

Once the bolts are out, gently pull the carburetor straight away from the engine. The old gasket—a thin rubber or cork seal between the carburetor and manifold—will likely stick to one surface or the other. Do not reuse this gasket. Scrape it off with a plastic scraper or old credit card, then wipe the mounting surface clean with a rag. Any gasket material left behind will cause the new carburetor to leak fuel.

If your engine has a fuel bowl drain plug at the bottom of the carburetor, you may see a small amount of fuel drip out as you remove it. This is old fuel trapped inside; let it drain into your pan and dispose of it properly.

Install the New Carburetor

The new carburetor should come with a fresh gasket and new mounting bolts. If it doesn't, buy a gasket kit for your specific carburetor model—they cost $5 to $15 and prevent leaks. Do not skip this step.

Place the new gasket on the intake manifold, then carefully position the new carburetor on top of it. Insert the mounting bolts by hand first, turning them a few threads to hold the carburetor in place. Once all bolts are hand-tight, use your socket to tighten them in a crisscross pattern (like tightening a car wheel), a quarter turn at a time. This ensures even pressure and prevents the gasket from squirting out. Tighten until snug—you don't need to crank hard; hand-tight plus a quarter turn is usually enough.

Reconnect the fuel line first. Push it onto the carburetor inlet until it seats, then tighten the hose clamp. The clamp should be snug but not so tight that you crush the rubber tubing. If you pinched the fuel line earlier, remove the clothespin now.

Reconnect the Throttle and Choke Cables

Refer to your photo to reconnect the throttle cable in exactly the same way it was attached to the old carburetor. The cable usually hooks into a small lever on the carburetor, and a bolt or clip holds it in place. Reconnect it, then check that the throttle lever moves freely when you pull the cable. It should return to idle position on its own when you release it. If it sticks, the cable may be kinked or the routing may be wrong—disconnect it and try again.

Do the same for the choke cable. Once both cables are connected, move them through their full range of motion a few times to make sure they operate smoothly. Stiff or jerky movement means something is pinched or routed incorrectly.

Prime the Carburetor and Test the Engine

Before you start the engine, you may need to prime the carburetor—that is, fill it with fuel so the engine doesn't have to suck fuel up from the tank on the first pull. Some carburetors have a primer bulb (a small rubber button on the side); squeeze it five or six times until you feel resistance, which means fuel has filled the carburetor. If there's no primer bulb, straightforward pull the starter cord several times without the spark plug wire connected. This draws fuel up without igniting it.

Reconnect the spark plug wire, set the choke to the cold-start position (usually a lever or knob marked with a snowflake or "cold"), and pull the starter cord. The engine may take several pulls to start because fuel is traveling through new passages. Once it fires, let it run for a minute, then move the choke to the warm position. If the engine runs smoothly and idles without stalling, the job is done.

If the engine won't start after ten pulls, or if it starts but runs very rough, stop and let it cool. Check that all fuel line connections are tight and that the throttle cable isn't stuck in the wide-open position. If you're unsure, take the equipment to a small-engine repair shop rather than risk damaging the engine.

Frequently Asked Questions

Can I reuse the old gasket to save money?

No. Old gaskets lose their seal and will leak fuel around the carburetor base. A new gasket costs $5 to $15 and prevents a much more expensive fuel leak or fire. Always replace it.

What if fuel leaks from the bottom of the new carburetor?

Stop the engine when ready and let it cool. The leak usually means the gasket wasn't seated properly or the mounting bolts are loose. Remove the carburetor, inspect the gasket for tears or folds, and check that the mounting surface is clean. Reinstall with a fresh gasket if needed.

Do I need to adjust the carburetor after I install it?

Most new carburetors come pre-adjusted from the factory and need no tuning. If the engine idles too fast or too slow, or won't idle at all, the adjustment screws may need turning—but this requires a tachometer and carburetor knowledge. A small-engine repair shop can do this for $30 to $50 if needed.

How long does a new carburetor last?

A quality OEM carburetor lasts as long as the engine if you maintain it properly. Use fresh fuel (not fuel older than 30 days), run the engine dry before storing it for winter, or add fuel stabilizer if you can't run it dry. These steps prevent the clogging that killed your old carburetor.

What if I lose a bolt during removal?

Do not start the engine with a missing bolt. Go to a hardware store and buy a replacement bolt of the same size and thread pitch—bring the old carburetor or a photo to match it. A missing bolt will cause vibration and may let the carburetor come loose while running.