How do I know if my lawn mower needs a new carburetor?

If your lawn mower is having issues starting, runs rough, or dies shortly after starting, it may need a new carburetor. Here are some signs that indicate it’s time to replace the carburetor on your lawn mower.

The Engine Won’t Start

One of the most common signs that a lawn mower needs a new carburetor is when the engine won’t start at all. When you try to start the mower, the engine may not turn over or it may turn over but not actually start up and run. Here are some things to check if your mower won’t start:

• Make sure you have fresh gasoline in the mower and that the fuel valve is turned on so gas can get to the carburetor.
• Check that the spark plug isn’t fouled or damaged and that the spark plug wire is properly connected.
• Try spraying a little carburetor cleaner or starting fluid into the air intake to see if that helps the engine turn over. If it does, it’s a sign there’s an issue with fuel delivery through the carburetor.

If the engine still won’t start after checking these basic issues, the carburetor may need to be rebuilt or replaced. The carburetor regulates the fuel-air mixture and if it’s clogged or damaged, it can prevent the engine from starting.

The Engine Starts Then Dies or Stalls

Another symptom of carburetor problems is when the mower starts up fine but then dies shortly after, often within a few minutes. Here are some potential causes if your mower starts up but then stalls out:

• Dirt, gunk, or debris in the carburetor blocking fuel flow. Small passageways inside the carburetor can get clogged over time.
• Incorrect fuel-air mixture. The carburetor jets or adjustment screws may be out of adjustment preventing proper mixing of fuel and air.
• Faulty gaskets or stuck float. This can impact fuel delivery and cause stalling.

If the mower runs fine once started but then quickly dies, inspect the carburetor. Cleaning and rebuilding it may resolve stalling issues. But a complete replacement may be needed if it is too damaged or cannot be adjusted properly.

The Engine Runs Rough, Surges, or Backfires

Erratic engine performance like surging, sputtering, or backfiring can also indicate carburetor trouble. Here are some potential issues if your mower runs rough or uneven:

• Obstructions in the carburetor jets or passages causing insufficient fuel flow.
• Air leaks drawing in extra air and throwing off the fuel mixture.
• Sticking float or inlet needle allowing too much fuel into the system.
• Incorrect adjustment of the carburetor screws and settings.

Running rough usually means the fuel-air ratio being delivered to the engine is off. Rebuilding and adjusting the carburetor or replacing damaged gaskets can often resolve these running issues.

The Engine Lacks Power

A lawn mower that lacks power, doesn’t reach full speed, or bogs down while cutting grass may also indicate carburetor trouble. Here are some things that can reduce engine power and performance:

• Insufficient fuel supply due to debris blocking carburetor jets or passages.
• Worn out carburetor parts like gaskets, diaphragms, and floats.
• Incorrect adjustment of the air-fuel mixture screws.

Replacing damaged carburetor components and adjusting the settings can restore full power. But if internal parts are overly worn or passages are badly blocked with varnish, a full carburetor replacement may be needed.

Visible Damage or Leaking

Inspect the exterior of the carburetor as well. Signs of damage like cracks or leaks can also indicate it needs to be replaced:

• Cracked or damaged carburetor housing.
• Leaking fuel lines or fittings.
• Sticking choke or throttle plates.
• Bent control levers or linkage.

A carburetor leaking fuel or that has damaged exterior parts should be replaced. Attempting repairs may not be worth it if the body of the carburetor is compromised or parts are severely damaged.

Diagnosing Carburetor Issues

Here are some steps you can take to diagnose carburetor problems further:

• Check for fouled or damaged spark plugs. Issues like oil deposits on the plug can mimic carburetor failure.
• Ensure adequate compression. Use a gauge to test engine compression.
• Make sure air filter is clean and unobstructed.
• Inspect fuel lines and filters for blockages.
• Look for visible issues like leaks, cracks, and loose parts.
• Clean carburetor passages using solvents or compressed air if clogged.
• Adjust carburetor screws and mixture settings based on factory specs.

Testing other engine components can help narrow down if the carburetor is truly the problem. Checking for leaks, obstructions, and doing adjustments may also resolve some issues before needing full carburetor replacement.

Cleaning a Carburetor

In some cases, a thorough carburetor cleaning can restore proper functioning without needing a complete rebuild or replacement. Here are the steps to clean a carburetor:

1. Remove air filter housing and air filter.
2. Disconnect fuel line from carburetor.
3. Remove carburetor from engine intake by unscrewing bolts.
4. Remove bowl at bottom of carburetor and clean with solvent.
5. Blow out carburetor passages and jets with compressed air.
6. Clean exterior surfaces like the throttle plate with a carburetor cleaner spray.
7. Rinse all surfaces and jets with fresh solvent.
8. Reinstall bowl and replace any gaskets.
9. Reattach carburetor and reconnect fuel line.

Taking these steps can remove built-up gum, varnish, and debris to get the carburetor working properly again. Just be careful using solvents and compressed air. Note that a full carburetor rebuild may still be needed if cleaning does not resolve issues.

When to Replace a Carburetor

Here are some signs that indicate it’s time to replace the carburetor completely:

• Engine still won’t start after diagnosing other issues.
• Carburetor is overly dirty with heavy varnish and debris.
• Gaskets, floats, and needle valves are worn out.
• Cracked, warped, or damaged carburetor body.
• Stripped screws that prevent proper disassembly and cleaning.
• Poor engine performance continues after rebuilding.

Replacing a very dirty or damaged carburetor is often easier and more effective than attempting to rebuild it. Quality replacement carburetors are available at reasonable costs for most mower models.

How to Replace a Lawn Mower Carburetor

Follow these general steps to remove and replace a carburetor on a standard walk-behind lawn mower:

1. Disconnect spark plug wire.
2. Empty fuel tank into approved container.
3. Remove air filter assembly.
4. Disconnect fuel line from carburetor.
5. Remove carburetor mounting bolts.
6. Detach throttle and choke linkage.
7. Remove old carburetor from intake manifold.
8. Install new carburetor with mounting gasket.
9. Reattach throttle and choke linkage.
10. Reconnect fuel line to carburetor.
11. Reinstall air filter assembly.
12. Add fresh fuel and reconnect spark plug.

Refer to the equipment manual for detailed steps for your specific mower model. Adjustment of linkage or governor may be needed on some models after installing new carburetor.

Finding Replacement Carburetor Parts

You can purchase a new carburetor or rebuild kit through several sources:

• Local small engine repair shops – They often stock parts for popular mower brands and models.
• Your mower’s manufacturer – Check their website or contact customer support to order direct.
• Online retailers – Sites like Amazon, Jack’s Small Engines, PartsWarehouse carry carburetor parts.
• Auction sites – eBay often has listings for complete carburetors or rebuild kits.

Search using your exact make and model number to find the correct replacement parts. Carefully compare any product photos and descriptions to your original carburetor to ensure proper fit and function.

Conclusion

Troubleshooting common engine issues like failure to start, stalling, running rough or lack of power will help identify if your lawn mower’s carburetor needs to be rebuilt or replaced. Cleaning varnish and debris from a carburetor’s jets and passages can sometimes resolve problems. But worn parts, significant damage, and continual performance issues will require complete carburetor replacement. Following proper disassembly steps and finding the right OEM or quality aftermarket replacement part for your particular make and model of mower will ensure success and have your mower running smoothly again.