How To Adjust A Lawn Mower Carburetor

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Gasoline engines are used in riding mowers to cut grass by spinning the blades and moving the mower forward. The gas flow from the fuel tank to the engine is managed by a carburetor on the engine.

The carburetor may become out of balance with regular use, resulting in less-than-ideal performance from the engine and mower.

In this guide, we’ll show you how to adjust a lawn mower carburetor to control the high speed, idle speed, and choke. Before you know it, your riding mower will be working at its best.

About Your Lawn Mower Carburetor

The first step to keeping your lawn mower’s carburetor in good working order is understanding what it does.

You probably already know that engines use the burning of fuel to create motion. More specifically, the heat energy produced by fuel combustion is used to drive motion. 

The fuel and air must be combined in order to generate the required amount of heat.  These mixtures are produced by carburetors. To maximize power and reduce fuel usage, they carefully balance the proportions of fuel and air. 

The length of time the engine has been running, the type of terrain you are driving over, and your speed are just a few of the variables that carburetors take into account while adjusting the air-fuel ratio.

The engine of your lawn mower may still run, but not at full capacity, if the carburetor isn’t operating properly. Engine power will be reduced if there is too much air and not enough fuel.

You will notice increased rates of fuel used when there is insufficient air and too much fuel. Your lawn mower won’t work at all if the balance strays too far in either direction.

Finding Your Lawn Mower Carburetor

The carburetor is typically located on the side of the mower’s engine on a riding mower. It often sits beneath or behind the air filter. To get to it, you must take off the filter and the housing for the air filter.

The carburetor can be found by following the gas line from the gas tank to the carb once the air filter housing has been removed.

What You’ll Need To Adjust Your Carburetor

You only need three items to adjust your lawn mower carburetor. Make sure you have them on hand before you access your carburetor.

You will need:

  • Protective gloves
  • Screwdriver
  • Carburetor spray cleaner
How To Adjust A Lawn Mower Carburetor

Adjusting The High Speed Mixture

  1. The high speed adjustment screw is located next to the idle speed adjustment screw. Depending on the manufacturer or the age of the carburetor, some may not have this adjustment option.
  2. To reach the carburetor, remove the air filter cover, filter, and cartridge.
  3. Start the engine, let it warm up for five minutes, then turn it off.
  4. Using a screwdriver, turn the high speed screw clockwise until the needle at the end of the screw reaches the seat.
  5. Turn the screw counterclockwise for 1 1/4 turns, being careful not to over tighten it.
  6. Start the mower engine by setting the throttle to a high speed. When the engine starts to slow down, turn the high speed screw first clockwise and then counterclockwise. Find the central point where the engine idles most smoothly.
  7. To test the modification, change the throttle’s setting from slow to fast and back to slow.
  8. Attach the nut to the mower after installing the cartridge, filter, and cover.

Adjusting The Idle Speed Mixture

  1. On the top of the riding mower engine, locate the air filter and air filter cartridge.
  2. To remove the air filter and cartridge, release the nut on the air filter cover after the engine has been turned off and allowed to cool.
  3. To clear the carburetor of any buildup of debris and grime, spray it with carburetor cleaner.
  4. Find the carburetor’s idle adjustment screw. Use a screwdriver to turn the screw clockwise until the needle at the end of the screw just touches the seat. The screw should then be rotated 1 1/2 times counterclockwise.
  5. Find the main jet adjustment screw at the bottom of the float bowl; depending on the brand and type, the carburetor you are working on may or may not have this.
  6. Turn the screw counterclockwise for 1 1/2 turns after it has been turned clockwise until the needle at the end of the screw just touches the base.
  7. Place the air filter cartridge and filter, but for the time being, leave the cover off.
  8. Start the engine, and then let it run at half throttle for about five minutes.
  9. Turn the idle screw slowly in both the clockwise and counterclockwise directions until the engine begins to slow. Locate the center where the engine idles most smoothly.
  10. Place the cover over the filter and cartridge and tighten it with the nut.

Adjusting The Carburetor Choke Linkage

  1. Find the choke linkage on the carburetor and remove the air filter cover, filter, and cartridge.
  2. Change the throttle’s setting to fast.
  3. Loosen the bracket holding the throttle cable’s casing in place. To release the cable, remove the bracket’s screw by using a screwdriver. Don’t remove the screw all the way.
  4. Your fingers should be able to move the cable until the carburetor’s choke plate closes. To fix the bracket in place, tighten it down against the cable casing while holding the cable in this position.
  5. Watch the carburetor’s choke plate open and close as you switch the throttle from fast and slow, then back to fast.

Final Thoughts

Adjusting your lawn mower carburetor is the key to keeping your mower functioning properly and efficiently. With this guide, you’ll be able to adjust every component of your carburetor so you can mow your lawn without hassle.

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