Fuel Not Getting From Carb To Engine

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Fuel not getting from your carburetor to the engine can cause abrupt engine shutdown, misfires, and may even prevent your mower from starting.

This is not an experience anyone would like to have, especially if you’ve got some work to do with your mower.

In this article, I talk about the reasons fuel may not be getting from your carburetor to the engine, and also share simple steps you can take to diagnose and fix this problem.

Reasons Why Fuel Is Not Getting From Your Carburetor To The Engine

If you notice that fuel is not getting to your lawn mower engine, you should first check to ensure that fuel is getting to the carburetor. 

If the carburetor is receiving fuel from the tank, the fuel may not be getting to the engine because of the following reasons:

  • Clogged carburetor jets
  • Float needle valve stuck in the close position 
  • Carburetor adjustment screw set too lean
  • Leaking carburetor gasket
  • Insufficient spark plug gap

Tools You Need For This Job

Some tools you may need to carry out the troubleshooting process effectively include:

  1. Work gloves
  2. Screwdriver
  3. Clean rag
  4. Compressed air
  5. Carburetor cleaner spray
  6. Carburetor repair kit
  7. Insulated pliers 
  8. Socket wrench
  9. Spark plug socket
  10. Multimeter

Fuel Not Getting From Carb To Engine: Diagnosis, Causes, and Fixes 

1. Clogged Carburetor Jets

The carburetor contains tiny openings called jets which allow fuel to enter and mix with the air. 

This produces a mist, which is subsequently transported to the combustion chamber of the engine and used to power your engine.

The holes in the carburetor jets are tiny and can easily get clogged with the sticky residue from stale fuel.

If this happens, the fuel will fail to mix with air and will be unable to get to the engine of your mower.

Diagnosis:

Check the carburetor bowls and jets. The presence of sticky residue indicates clogging.

Fix:

Soak the carburetor in a carburetor cleaner for at least one hour to clean it and unclog the jets.

Clean the carb and allow it to dry. Use Blow through the hets and holes with compressed air to remove any remaining debris. Then install it back in the mower.

2. Stuck Carburetor Float Needle

The carburetor float needle valve can get stuck in the closed position and prevent fuel from getting into the engine.

Your carburetor’s needle valve will not allow fuel to flow to the engine properly if it is rusted or stuck. You’ll need to clean the carburetor and, if necessary, replace any worn-out components.

Diagnosis:

  • First, take out the carburetor
  • To access the carburetor interior, remove the float bowl from the carburetor. 
  • The pin keeping the float in place can then be removed.
  • Before you do that, you can try moving the float and needle with your hands up and down; it should move easily and with little resistance.
  • If there is resistance, it is stuck.

Fix:

Replace the float needle. In most cases, you don’t need to replace the float, but I recommend giving it a thorough cleaning.

You can try using a carb cleaner to clean the needle valve. Simply soak the item and let it stay for a few hours in the carburetor cleaner.

Then, wipe it off and let it air dry properly for some time. 

3. Carburetor Mixture Screw Set Too Lean

You should also check the carburetor adjustment screw if you notice that fuel is not getting to the engine.

An engine’s carburetor has a specific screw called an air-fuel mixture screw that regulates how much air is mixed with the fuel. 

Oftentimes, this adjustment isn’t set correctly, preventing the engine from receiving the required air/fuel ratio to function effectively.

This is because these screws regulate how much fuel gets into the engine, and if they aren’t adjusted properly or set too lean, the engine will receive little to no fuel.

Diagnosis:

Locate the air-fuel mixture screw and use a flathead screwdriver to check how tight it is.

If it is too tight, the screw may be set too lean.

Fix:

Readjust the screw to allow more fuel into the engine.

How To Adjust The Carburetor Air-Fuel Mixture Screw

  • Turn off the engine and let it cool
  • Remove the air filter housing and air filter 
  • Locate the adjustment screw on the side of the carburetor. You can consult your owner’s manual to find the screw
  • Rotate the screw clockwise with a screwdriver until you feel a resistance
  • Turn the screw in the opposite direction for about 1½ turns to fine-tune it
  • Reassemble the air filter 
  • Start the engine and readjust if necessary

4. Leaking Carburetor Bowl Gasket

The carburetor works by introducing fuel at the highest point of vacuum and airflow to mix it in precisely the right amount with the air. 

It does this by sucking fuel through the carburetor’s metering jets at a high vacuum. 

Although a leaking carburetor gasket might not let fuel escape, it will allow air to enter where the vacuum is most important. This may cause issues in delivering fuel to the engine.

Diagnosis:

Inspect the carburetor gasket for cracks or signs of wear.

Fix:

Replace the gasket if it is split or worn out.

5. Insufficient Spark Plug Gap

Problems with your spark plug can disturb the normal running process of your mower and may prevent fuel from getting to the engine.

Ensuring your spark plug’s center electrode and grounded electrode have the proper space between them is extremely important and should not be overlooked.

Over time, spark plugs get worn out and their gaps can be altered. If this happens, the plug will produce less spark than required by the engine and this can make the engine lose compression and be unable to receive fuel.

Fortunately, if you have the correct instrument on hand, it’s very simple to inspect and adjust the gap in your spark plug.

Diagnosis:

You’ll need a multimeter to check if your spark plug is gapped correctly

  • First, remove the spark plug
  • Use a clean rag to wipe off dirt from the plug
  • Conduct the test using a multimeter

How To Test A Spark Plug Using A Multimeter

  • Set your multimeter to either 10k, 20k, or higher, in ohms
  • Take a multimeter lead and place it against the metal tip where the spark plug hood snaps (the terminal).
  • Next, place the other multimeter lead right on the spark plug electrode’s tip. The spark plug’s electrode is located on the side that screws into your engine.
  • Instead of resting on the cylindrical side of the electrode, you want your multimeter lead to be resting at the electrode’s flat top or tip. It’s crucial to do this correctly so that you can get a reliable reading.
  • Check the reading on the multimeter.

A working spark plug from a lawnmower or small engine should register between five and fifteen thousand ohms.

If the reading falls within this range, your spark plug is good. If not, you need to change it.

You can also conduct a visual spark plug test if a multimeter is not readily available.

Fix:

Replace the spark plug if it is not producing enough spark.

Conclusion 

If your engine runs rough, shuts down abruptly, misfires, or refuses to start, the engine might not be receiving fuel from the carb.

This could be a result of clogged carburetor jets, stuck float/needle valve, adjustment screw set too lean, leaking carburetor gasket, or malfunctioning spark plug.

Using the troubleshooting guide in this article, take your time to find out the exact cause of the problem and then, apply the recommended fix to solve the problem.