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Lawn Mower Won’t Start After Cleaning Carburetor

The carburetor is a vital component but not the only part involved in starting a lawn mower. A visibly clean carburetor is not necessarily in flawless working condition. Therefore, you have to conduct a thorough inspection when your lawn mower won’t start after cleaning the carburetor. 

A lawn mower won’t start after cleaning the carburetor if the part is worn, broken, or installed incorrectly. You may also have a cracked primer bulb, a malfunctioning spark plug, a clogged air filter, or bad gas. Furthermore, inspect the main engine components to fix the problem. 

Assess the current condition of your carburetor and the last cold start performance of the lawn mower. These considerations will help you eliminate a few typical problems in lawn mowers. Read on to know about the usual glitches to detect and fix them. 

Why a Lawn Mower Won’t Start After Cleaning the Carburetor

Ensure your carburetor is thoroughly clean and dry before you reinstall it on the lawn mower. Ideally, you should use a quality carb cleaner and dry it with compressed air. Check if the carburetor’s parts are in good condition; an easy inspection when you clean them separately (source).

You may consider the following probable issues chronologically to detect the causal problem. 

The Carburetor Has Worn and Broken Parts or Is Installed Incorrectly

A lawn mower carburetor has several small parts, such as:

  • Venturi
  • Inlet and outlet ports, including jets
  • Diaphragms and valves
  • Metering unit, including lever, needle, pin, and spring
  • Nuts, screws, gaskets, seals, etc. 

A worn out or broken metering unit will prevent the carburetor from starting your lawn mower, even if it is visibly clean. Likewise, corroded jets and venturi won’t function optimally. Additionally, you may have a clogged valve or damaged diaphragms. Check the gaskets or seals, too. 

Furthermore, you must install the carburetor correctly. The nuts and screws should have a snug fit. Pay heed to the fastening bolts and the adjustable screws if your lawn mower has the latter. Many contemporary lawn mower models have air mixture and idle screws. 

You may replace a few broken carburetor parts, such as the metering unit. However, if you have significant corrosion, the only solution may be replacing the carburetor. 

The Carburetor Is Not Sufficiently Primed for the Engine To Start

Many lawn mowers have a primer bulb to assist the engine’s cold start. The purpose of this primer bulb is to pump a bit of gas or fuel into the carburetor. Subsequently, the carburetor mixes the fuel with air and combusts the mixture to start the engine when you pull the cord. 

When you reinstall a cleaned and dried carburetor on your lawn mower, there is no fuel inside it, and thus it will not start the engine. The standard practice is pressing the primer bulb a few times to pump or draw sufficient fuel into the carburetor, depending on the model. 

However, you cannot do this if the primer bulb is cracked or broken. Evident cracks or signs of damage are easy to spot, but tiny leaks are difficult to detect visually. Unfortunately, many lawn mowers don’t have transparent primer bulbs, so you cannot see the fuel level inside. 

Here’s how you can inspect and fix a primer bulb:

  1. Replace the primer bulb if you find visible signs of cracks or damage. 
  2. Otherwise, press the primer bulb to feel its compression and retraction. 
  3. A soft compression and delayed retraction implies structural damage or leaks.
  4. Replace a leaky primer bulb, including the valve on the lawn mower, if it is also broken.
  5. If none of these is a problem, check for fuel or gas inside the carburetor.
  6. Inspect the gas lines if there is no trace of fuel inside the carburetor, despite priming. 
  7. Check the fuel lines and clean them if the primer bulb and carburetor are working.
  8. Replace leaking or damaged fuel lines if they are the problem preventing the cold start.  

The Spark Plug Is Dirty, or the Air Filter Is Clogged

A clean and primed carburetor won’t start your lawn mower if the spark plug fails or the air filter is clogged. You may have both these problems simultaneously. Replace a broken spark plug and an unusable air filter. Otherwise, clean and reinstall them to check if the lawn mower starts.  

Here are the steps to clean and test a lawn mower spark plug:

  1. Remove the spark plug from the lawn mower. 
  2. Clean the carbon buildup from the spark plug with a soft wire brush. 
  3. Get a multimeter and test the two ends of the spark plug for resistance. 
  4. Replace the spark plug if it has no resistance, thus implying it is broken. 
  5. Check the spark plug part number to buy an identical one.

Watch this video to test if your lawn mower spark plug is alright or broken:

How to Test a Spark Plug In One Minute

There Is Bad Gas in the Lawn Mower’s Fuel Tank

No or low fuel is not a complicated problem. You can refill gas into the tank and try to start your lawn mower. However, you may not succeed if you have bad gas in the tank and fuel lines. Gas goes bad when it is stored in the fuel tank for a long time, especially if it is idle for an entire season. 

Many lawn mowers have a carb bowl connected to the fuel line from the gas tank. This carb bowl may get dirty, and the main jet could be clogged as a result. Thus, you need to get rid of the bad gas from the fuel tank, line, and carburetor bowl (source).

How Do I Get Bad Gas Out of a Lawnmower?

You can get bad gas out of a lawnmower by detaching the fuel hose from the carburetor and draining the stale fluid to a pan. Alternatively, use a siphon hose to pump the bad gas out of the fuel tank. Tilt the lawnmower backward or the opposite side of the carburetor to remove bad gas. 

Many lawn mowers have a hole or drain plug on the deck. You can use such a feature to get bad gas out. Consider the following process:

  1. Place a large pan or container under the lawnmower to collect the drained gas. 
  2. Use pliers to remove the fuel hose clamp connecting the line to the carburetor. 
  3. Alternatively, use the drain plug (if available) and let the bad gas flow out of the fuel tank.
  4. Allow all the bad gas to flow out of the fuel tank through the hose or drain plug.
  5. The pan under the lawnmower or container hooked to the drain plug collects the gas.
  6. Unbolt the carburetor bowl and let bad gas flow out of the small reservoir. 
  7. Clean the jet holes on the carb bowl nut with a thin wire or compressed air.
  8. Clean the fuel tank, hose, and carb bowl before filling with fresh gas. 

Here’s one way to get bad gas out of your lawn mower:

Lawn Mower Repair - How To Drain Bad or Old Gas and Clean Carburetor Bowl and Jet

You can also remove the fuel tank cap and use a siphon hose to pump out the bad gas. If you have to tilt the lawn mower at any time, do so backward or to the carburetor’s opposite side. Otherwise, you may have engine oil flow into the carburetor, and you will have to clean it again. 

Final Thoughts

Your lawn mower won’t start after cleaning the carburetor if any critical engine parts are broken, such as the motor or flywheel key. Check these components and to get your lawn mower back to working condition.