So you walk up to the garage, open the door, and wham…it hits you! The smell of gasoline fills the garage air and notice the culprit is your lawn mower. So you need to check it out. First thing is to roll the mower out of the garage into a well ventilated area.
Your mower may smell like gas because of a bad gasket around the fuel cap, leaking fuel lines, leaking filter, and dirty carburetor. A bad gasket around the bowl of the carburetor, cracked primer bulb, cracked fuel tank or bad gas can also cause your mower to smell like gas.
It is important to find the reason fuel is leaking or escaping from your lawn mower. Here are some items you will want to check to find the lawn mower gas leak.
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Follow all safety instructions provided in your equipment operator’s manual before diagnosing, repairing, or operating. Consult a professional if you don’t have the skills, or knowledge or are not in the condition to perform the repair safely.
Reasons Your Lawn Mower Smells Like Gas
1. Bad Gasket Around the Fuel Cap
A gas cap is normally vented so you usually get some fuel smell out of the cap, but there shouldn’t be enough odor coming out of the gas cap area to fill the garage. Remove the gas cap and inspect it for cracks. You will also need to look at the gasket inside the cap.
Gaskets in fuel caps can get dry and brittle over time. You will want to make sure the fuel cap gasket is not wrinkled, torn, or shrunk down a bit. Wipe the gasket and cap down, and replace the gasket if needed. If the gas cap is cracked you will need to purchase a replacement.
2. Leaking Fuel Lines
Locate the fuel lines next. Follow the fuel lines and look for leaks. You may find residue that may be holding fuel around the clamps. If this is the case, you will need to remove them and install new clamps and fuel lines. Check for punctures in the fuel lines or debris build-up.
3. Leaking Fuel Filter or Cracked Fuel Pump
You will also want to look at the fuel filter housing. It isn’t unusual to find the plastic fuel filter housing cracked. Replace the fuel filter if you find it leaking fuel. Check the fuel pump to ensure it isn’t cracked and fuel isn’t running down the fuel line.
4. Dirty Carburetor
Take a look at the carburetor. The mower’s carburetor has a vent on it, but it should not leak fuel. The carburetor may begin to leak if it becomes dirty or if the float is stuck.
If this is the case, you will have to remove and clean the carburetor. A stuck float needle will allow fuel to overflow.
Steps to Clean Your Lawn Mower Carburetor
- Spray carb cleaner to minimize carbon buildup. Remove the air filter and spray some carb cleaner in the air intake. Start the engine to see if it will run. If your mower fires up and still won’t stay running then we need to get inside the carburetor.
- Gather pliers, screwdrivers, sockets, and ratchets so you don’t destroy parts while taking the carburetor apart.
- Take a photo for reassembly. These days most people have a handy camera on their phones. It’s a very good idea to take a picture of the carburetor so you can refer to it if you don’t remember how to reassemble it after tearing it apart. You will want to make sure you get a photo showing how the linkage and springs go back on the carburetor.
- Remove the throttle cable and choke cable if your mower has one.
- Undo the filter housing and nuts or screws that hold the carburetor.
- Slowly remove the springs so you don’t stretch them out too much. You may have to twist the carb a bit to get the springs off. Also, watch the gasket at this point so you don’t tear it. This is the gasket located between the engine block and the carburetor.
- Remove the bottom screw from the float bowl. The float bowl is where gasoline is stored inside the carburetor. It should have gas in it so have a rag ready to catch the gas.
- Remove the bowl being careful to not damage the o-ring around it. Caution: Do not get any carb cleaner or any other chemical on the o-ring. It will stretch out and you won’t be able to reuse it.
- Inspect the stem for clogged holes. This stem hangs down from the center of the carburetor and has holes in it. If these holes get plugged from old fuel it will not draw fuel up to the jet. If the holes are plugged, take a thick wire to clean them out. It’s easier to see what you’re doing if you use a flashlight. Once you get the holes clean you can rinse them with carb cleaner.
- Inspect the carburetor for hard crusty white buildup. This white buildup is fuel additives including ethanol. You need to try to get as much of the white power material out as you can. It’s nearly impossible to get it all out.
- Reassemble the carburetor now that the carb is clean. Put it back together in the reverse order you took it apart. Remember to refer to the photo you took of the carburetor when reassembling so all parts are reinstalled in the right places.
- Add fresh fuel plus a fuel stabilizer before you start your mower. Pour the fuel into the tank and give it a chance to fill the bowl of the carburetor. Start your engine. If you are starting with a pull cord, give the rope a yank. It may not start on the first pull, but it should start after several pulls and continue to run.
5. Bad Gasket & Residue Around Bowl of Carburetor
If you find residue around the bottom of the carburetor, you will want to replace the gasket. The bottom of the carburetor is also referred to as the carburetor bowl.
Replacing the small rubber gasket at the bottom of the bowl is a very simple process. You will need to get the make, model, and spec number off of the engine and take it to your local dealer to get the correct o-ring gasket for your lawn mower.
Once you have the replacement gasket, shut the fuel off to your mower. Unscrew the screw and drop the bowl down.
Replace the gasket and reinstall the bowl and the screw. Turn the fuel back on and wipe down the carburetor bowl and make sure there are no more leaks.
6. Cracked Primer Bulb
Your mower may use a primer bulb that may begin to leak. Primer bulbs are made from rubber and will get dry and brittle over time. Replace your primer bulb if you notice it becoming dry or beginning to crack.
7. Cracked Fuel Tank
Fuel tanks are made from polyethylene. This material is used because it withstands the chemical makeup of fuel and doesn’t break down. Lawn mower fuel tanks seem to hold up well over time.
They still may get impacted and crack. Something could fall off them or you may hit something with your mower and impact the fuel tank. Check for signs of damage and fuel leakage.
8. Bad Fuel
Gasoline only has a shelf life of about 30 days. When gas is getting old it is going to develop a stronger odor. It’s important to not store fuel longer than 30 days. You will also want to consider the gas station you are getting your fuel.
It’s best to get fuel from a busy high-traffic gas station that is consistently refueling and bringing in fresh fuel. Don’t go to the small gas station in the middle of nowhere.
If you are unable to use the fuel quickly, add some fuel stabilizer additives to your fuel cans before you fill them. This is added protection against bad fuel as your store it in the winter or even in the summer’s heat.
Gasoline has a very distinct odor to it. The fumes are known to rise about 7″ or so before they dissipate. Keep in mind the odor should not be a heavy smell in the garage. If you can’t find a leak you should get into your local repair facility to have the fuel leaks repaired.
Why Does Gas Leak from My Lawn Mower Carburetor?
Gas may leak from your lawn mower carburetor because the float is stuck and doesn’t regulate the amount of fuel in the carburetor which may overfill and leak out of the carburetor.
The float in the carburetor literally floats on top of the fuel that is in the bowl. The float allows gas to fill the carburetor without overfilling.
The float may get stuck because it becomes dirty and gummed up from buildup from chemicals in your gasoline. It is important to keep the carburetor clean and running properly.
Using the right kind of gas is key to minimizing these deposits and keeping your lawn mower carburetor clean. You will need to clean the carburetor to remove the dirt and gummy buildup.
Can Gas Cause My Lawn Mower to Smoke?
Your lawn mower may smoke if the wrong fuel is used or the fuel is mixed with another substance.
- Make sure you are using the correct gas in your lawn mower. It needs to be fresh. Use a fuel stabilizer in your fuel if you will not be using it within 30 days.
- If your lawn mower is smoking, there may be other reasons for the cloud of smoke coming from your machine. You could have a clogged filter, insufficient oil level, or other engine problems such as a valve train or piston ring problem.
Still Having Problems with Your Lawn Mower?
Lawn mower ownership doesn’t come without its frustrations. Own a mower long enough, you are bound to run into many lawn mower problems including starting, smoking, leaking, cutting, and overheating.
For mower troubleshooting, check out my guide Common Lawn Mower Problems: Solved.