Similar to an automobile engine, a small engine on a self-propelled lawn mower, push mower, or riding mower uses a carburetor to help run the engine. The lawn mower carburetor ensures that the proper mixture of fuel and air will enter the engine cylinder to allow for combustion. When ignited by the spark plug, the fuel and air mixture will combust, forcing the engine piston downward which rotates the crankshaft causing the lawn mower blade to spin and, if applicable, the lawn mower wheels or riding mower wheels to rotate.
Old or bad fuel can leave a gummy residue inside the carburetor. This residue can create a restriction or clog, preventing the proper ratio of fuel and air from entering the engine cylinder. When this happens, we often refer to the carburetor as being “dirty”.
Dirty Carburetor Symptoms
A dirty or restricted carburetor is fairly easy to diagnose:
- The lawn mower engine has trouble starting.
- The engine starts but stalls while you’re cutting the lawn.
- The engine runs rough during mowing.
- Black smoke is seen coming out of the muffler.
- There is a noticeable increase in fuel consumption during normal lawn mower use.
You can avoid causing a restriction in the carburetor by always using fresh fuel when you fill the tank, along with a fuel stabilizer to help maintain the quality of the fuel. If the carburetor does become clogged, you should consider cleaning the component.
Cleaning the lawn mower carburetor
In order to fully clean the carburetor, you will need to uninstall it from the lawn mower engine. While this process will vary depending on the mower model, you can use these steps as a general guide.
- Before you begin, make sure the mower engine has cooled.
- Remove the engine cover if necessary.
- Remove the air filter cover, the filter itself, and the air filter housing.
- Shut off the fuel valve, if available, or crimp the fuel line then detach it from the carburetor – be prepared for some fuel to spill.
- Detach the choke and throttle linkages from the carburetor throttle lever.
- Slide the carburetor off the mounting bolts.
- Unthread the screw to release the carburetor bowl, if applicable.
- Remove the float pin to release the float and needle.
- To fully disassemble the carburetor, you may need to unthread screws to release the primer bulb and base, then remove a metering plate, gaskets, and diaphragms.
- With the carburetor intake and outlet ports exposed, you can spray a dedicated carburetor cleaner, or WD-40, into the ports to clean out any residue.
- Clean out the bowl as well, if applicable.
- If the carburetor itself shows signs of rusting, use sandpaper to remove the rust.
- Allow the carburetor to dry, then reassemble it, making sure to properly position the diaphragms, gaskets, metering plate, and primer base as required, along with the float needle and float.
- Make sure the bowl gasket is in place then reinstall the bowl if necessary.
- Slide the rebuilt carburetor back onto the mounting bolts and attach the throttle linkages to the throttle lever.
- Reattach the fuel line to the carburetor.
- Reinstall the air filter housing, along with the air filter and filter cover.
- Reinstall the engine cover if necessary.
Is cleaning the carburetor enough?
In addition to cleaning a carburetor, you should consider purchasing a carburetor repair kit to replace some of the major carburetor components like the float and float needle, gaskets, and diaphragms. If the carburetor still performs poorly, you may need to replace the old carburetor with a new one. Be aware that a dirty air filter or a clogged fuel filter can also cause a lawn mower engine to stall or run rough. As part of your annual lawn mower maintenance, you should always replace the air filter and fuel filter with new ones.
Find the right parts with Repair Clinic
Whether you own a Craftsman lawn mower or riding mower, a Honda lawn mower, a Murray mower, or a Snapper model, Repair Clinic.com stocks the specific parts that fit your equipment, including Briggs and Stratton carburetors. To find the right parts, enter the full model number of your lawn mower, or the mower’s engine, in the Repair Clinic.com search bar. The navigation filters on the left side of the part results page will allow you to refine your search down to just the part or parts you’ll need.