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Honda Lawn Mower Carburetor Adjustment: How to Do It

When your Honda lawn mower’s engine doesn’t idle, lacks power at high speed, or won’t start, it could be time to adjust the carburetor. If you have never done this before, you are probably wondering how difficult it will be, what tools you will need, and if you should just call an expert.

To adjust a Honda carburetor, start by warming up the engine. Next, locate the carburetor and find the adjustment screw. Turn the screw clockwise until the engine begins to stall, then counterclockwise until it sounds rough. Find the midpoint between these two extremes for optimal performance, ensuring a smooth and efficient ride.

Beginning with a warm engine is crucial as carburetor adjustments in a cold engine might result in a lean mixture when it gets hot. Once the engine is warm, locate the carburetor, which is usually situated behind the air filter. Ensure to wear safety gear, like gloves and goggles, to protect yourself during the adjustment. When adjusting the screw, use a tachometer to note the RPMs (revolutions per minute) at which the engine begins to sound abnormal in both clockwise and counterclockwise directions. The optimal performance point is usually at the highest RPM before the engine sound changes.

It’s essential to note that carburetor adjustments should be made in small increments to prevent drastic changes in engine performance. After finding the midpoint, test the engine at various speeds to ensure it performs well under different conditions. If the engine doesn’t perform as expected, slight tweaks might be needed to fine-tune the adjustment. Always refer to the specific Honda model’s manual for any model-specific instructions or warnings to ensure safe and accurate adjustments. If you’re unfamiliar or uncomfortable with performing a carburetor adjustment, seeking professional assistance is advisable to ensure optimal and safe engine performance.

How Does a Carburetor Work?

How Does a Carburetor Work?

Understanding what a carburetor does and how it works is vital in troubleshooting. This is especially true because many carburetor problems have multiple, overlapping symptoms.

The carburetor’s role is to provide the space where gas and air mix. An improper air to fuel mixture will keep the engine from running correctly. An incorrect gas and air mix cause most carburetor problems. Your job is to figure out what is causing the mix to be off.

  • Float Chamber: The float chamber holds fuel, and as the amount of fluid increases, the float rises until it is pushed into its seat. When fuel leaves the chamber, the float falls. As more fuel enters, it rises again.  
  • Intake:  Air rushes through the throat of a carburetor, and then a narrower passageway called a venturi. This causes the air to speed up, creating a vacuum that pulls fuel into the fuel nozzle.  
  • Fuel Jet: Once the proper gas/air mixture has been created, the fuel is pulled through the fuel jet. This creates the explosion that powers the engine.
  • Throttle Valve:  This valve controls the amount of gas that goes into the carburetor. An open valve increases the engine’s power, and a closed valve stops the engine.

Carburetor problems can occur at each of those points, and the way to fix most carburetor problems is to get inside and see which of these is causing the problem. 

Why You Should Clean the Mower’s Carburetor

Why You Should Clean the Mower's Carburetor

Although you might be tempted to play around with the throttle or make other adjustments, clean the carburetor. Otherwise, any corrections you make will be temporary, and you could wind up causing even more damage to the carb.

Also, get a parts cleaner, such as WD-40 Specialist Carb/Throttle Cleaner. It contains the solvents you need to clean out the gunk, and the spray will blast away dirt and deposits. For tools, you will need screwdrivers and a socket wrench.

Mower Engine Starting Problems

Mower Engine Starting Problems

If your engine is not starting, you have difficulty starting it, or it stops after you get it started, then the following could be causing starting problems:

  • The main jet, main nozzle, or main nozzle air path could be clogged.
  • The float isn’t moving correctly.
  • The throttle stop position is wrong.

Mower Speed Problems

Mower Speed Problems

If the engine speed does not increase, the speed is unstable, or the engine performs poorly at high speed, then an additional clog to check for is the pilot jet—either its air path or the jet itself are clogged.  

Should speed problems happen at low speeds or the idle speed is unstable, then in all likelihood, the pilot jet or its air path is clogged. You will need to check for dirt and clean.

Copyright article owner is for this article. This post was first published on August 27, 2020.

Mower Gasoline Problems

Mower Gasoline Problems

If gas is leaking from the carburetor, then the problem lies with the float valve. Either the float valve is worn out or coated with dirt, or the valve seal is worn or dirty.

Getting to the Mower’s Carburetor

Getting to the Mower's Carburetor

Before you get started, we recommend you disconnect the spark plug cap. This is to prevent the mower from accidentally starting. Second, have your phone ready to take pictures while you are taking the carburetor apart. 

Fix Without Taking the Carburetor Apart

You might get lucky and avoid having to take the carburetor apart. To do so, focus on cleaning out the carburetor idle jet. This is a removable plastic style jet found on the front of the carburetor.  

  1. First, spray the carb cleaner and remove the dirt and gunk. 
  2. Look for a plastic screw with a Phillips head bolt. That’s the idle adjustment screw. Loosen and remove it.
  3. Now you will have access to a rubber plug with a hole. This is the idle/pilot jet. 
  4. To remove the pilot jet, you need to pull it out gently. Use flathead screwdrivers to wedge it up. 
  5. After you get it out, you should clean it with the carb cleaner. The small hole on the end often gets plugged. Honda makes Jet Cleaner sets, but a tiny pin will be a good substitute.
  6. After you have cleaned the pilot jet, push it back in carefully, and then replace the idle screw. Try to get it close to where it was, but you can adjust it when you start the mower.

Clean Out the Float Bowl

The float bowl is at the bottom of the carburetor. It is easy to take off, but before you do, turn off the fuel line. Then loosen the bolt on the bottom and take out the bowl. 

There are two gaskets—one where the bowl connects to the housing, and another one on the bolt. Inspect both for cracks. Then clean out the bowl and replace the housing.

Taking the Mower’s Carburetor Apart

Taking the Mower's Carburetor Apart

If the mower is still not running correctly, then the carburetor must be taken apart so that you can clean it. This is a much more complicated procedure and could take an hour or more.

  1. First, remove the air filter. If it is dirty, replace it. A dirty air filter can affect how well your mower runs better. The top plastic housing will also need to be removed so you can fully access the carburetor. 
  2. Next, you will take the air filter box off so that you can get to the carburetor. In most models, it is held on by two bolts. As you loosen the bolts, hold onto the carburetor. The bolts run through the carburetor and mount it to the motor housing.
  3. Now that you have access to the carb, get ready to start taking pictures. Anything you unhook needs to be hooked back correctly. Keep an eye out for the tiny spring attached to the top.  
  4. Once you have taken the carburetor off, it is time to disassemble. As you do so, check the gaskets—worn ones need to be replaced. Continue taking the carb apart and cleaning. Every hole needs to be clear of dirt.  

Finally, the carburetor will have to be reassembled. Hopefully, you took lots of pictures so that you have them as guides.  

Rather than taking a carb apart, some folks simply buy a new carburetor. Be sure to check compatibility with your Honda Mower.

Check out this 12-minute video that will take you through the steps of fixing a lawn mower carburetor:

Fuel Recommendations for Honda Small Engines

Fuel Recommendations for Honda Small Engines

To prevent future problems, make sure you are following Honda’s recommendations. Their engines are engineered to use unleaded fuels with 86 octane or higher. Ethanol fuels can be used as long as the fuel has no more than 10% ethanol (E10). A fuel with methanol should contain no more than 5% methanol.

Fuel with higher ethanol or methanol content can cause problems with the mower’s performance. The engine’s warranty does not cover damage to the engine caused by fuel with more than 10% ethanol.  

If possible, regular unleaded gasoline is ideal. Avoid E85 at all costs because Honda considers it an alternative fuel since it is 85% ethanol and only 15% gasoline.

Storage Suggestions to Prevent Carburetor Problems

Storage Suggestions to Prevent Carburetor Problems

These are some suggestions to prevent future carburetor problems. Gasoline can begin to deteriorate within three to four weeks, so use these if you only mow every couple of weeks:

  • Fill up the tank. As fuel is exposed to heat or air, it oxidizes and can gum up the carburetor’s jets. Keep the tank full to minimize how much gas can enter the tank through the vent.
  • Run the engine out of gas. No fuel = no oxidation. If the mower only has a little gas in the tank, run it dry and close the fuel valve.
  • Storage container. Make sure you close the container tightly and store it in a cool place. Honda discourages metal fuel containers since they might rust, and tiny rust particles can clog the carburetor.
  • Fuel Stabilizer. Fuel stabilizers should be added if gas is stored either in the container or the mower for three months or longer. If you plan to use the mower within a year, there is no need to drain the gas from the fuel tank or carburetor—as long as you add the stabilizer.

Final Thoughts

Carburetors are an essential and often overlooked part of a lawn mower. If your mower is not running well and you have checked the air filter and spark plug, you might have to work on the carburetor. Taking the carburetor apart and cleaning it is time-consuming but not difficult. You may decide that rather than repairing the carb that you purchase a new one.

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