Lawn Mower: Starts But Immediately Dies

If your lawnmower’s engine will fire but then immediately dies, it could be a problem with the carburetor. A small engine needs a constant supply of fuel and air to start and run. The carburetor regulates the amount of fuel that enters the engine and mixes the fuel with air into the perfect ratio needed for combustion. Typically, this problem is caused by a blockage in the carburetor. Dirt or other debris can easily plug the tiny openings in the carburetor. Fuel left sitting in the carburetor for long periods of time will thicken into varnish, plugging the carburetor. Fuel with ethanol will cause corrosion when it sits unused. A thorough cleaning of the carburetor will usually get your mower running again. To begin cleaning your carburetor, remove it from the lawnmower and carefully disassemble its components. Remove the bowl and drain any fuel out of it. Notice that there is a gasket that seals the bowl to the carburetor as well as one to seal the bowl screw. If either gasket is damaged or cracked, it should be replaced. Remove the pin that the float pivots on and the metering needle. The metering needle should be inspected for corrosion and wear on the tip of the needle. Dirt or corrosion on the tip or the needle seat will prevent the needle from closing completely. This will cause fuel to continue to flow into the bowl and spill out of the carburetor’s throat. Remove the main jet and the emulsion tube. Dirt or corrosion can clog the tiny opening in the jet or the series of holes cross drilled in the emulsion tube. These tiny openings can be cleaned with carburetor cleaner and compressed air. Fishing line can be used if needed to help clean debris out of the openings. Never use anything metal when cleaning a carburetor. Metal picks, wires, or other tools can easily alter the size of the openings changing the amount of fuel that can flow through them. Next is the pilot jet. There will often be a plug or screw on the carburetor’s body that covers the pilot jet. Access the pilot jet and clean it with carb cleaner, compressed air, and fishing line if needed. Once the carburetor has been stripped down you can clean the carb body and bowl. Use carb cleaner to thoroughly clean each tiny passage in the carburetor. Also clean the bowl, main jet, pilot jet, and emulsion tube with the carb cleaner. Use compressed air to remove any residual carb cleaner from each component. If you have an ultrasonic cleaner in your arsenal of tools it will work great to clean your carburetor. Ultrasonic cleaners do an amazing job of cleaning the tiny openings and passages in a carburetor. Often times an ultrasonic is the only way to save a badly plugged carburetor. Replace any part in the carburetor that was too dirty to clean or that was damaged by corrosion. Carefully reassemble the carburetor after cleaning and reinstall it onto the mower. If you are unsure about disassembling a carburetor for cleaning, you can always just replace the entire carb. It is always a good idea to check the price of a new carburetor before tackling a cleaning project. Some carburetors are very affordable making it hardly worth the time required to clean it verses simply bolting a new one in place.

The air filter removes any dirt or debris from the air before they can enter the carburetor and the engine. There are many different types and styles of air filters, but they all perform the same job. If your lawnmower’s engine starts but then immediately dies, its air filter may be plugged. The engine requires a constant supply of air and fuel to start and run. As the air filter becomes plugged, the flow of air is restricted. The first signal that the air flow has been reduced will be black exhaust smoke as the air/fuel ratio becomes rich with fuel. As the filter becomes more plugged the engines performance will drop off and there will be a noticeable reduction in power. If not serviced, the filter will become so clogged that the engine will start and immediately die or simply won’t be able to start at all. Servicing the air filter is a simple repair and is something that should be done at least once per year. The air filter will be located behind the air filter cover on the side of the engine. The cover is typically held in place by knobs, screws, or locking tabs. Remove the cover to access the filter. With the cover out of the way, you can remove the filter from the filter base. Lawnmower air filters will typically be either a pleated paper or felt type or a sponge foam type. It is best to simply replace the pleated-style filter. It is possible to use compressed air to blow debris out of a pleated filter, but care must be taken to not damage the filter while cleaning. Even a small tear in a filter will let enough debris into the engine to plug the carburetor or cause cylinder and piston damage. Foam filters can be cleaned multiple times using water and liquid dish soap. If the filter is beginning to break down and pieces of foam are coming loose, it should be replaced. Once washed, allow the filter to dry. Before a foam filter is reinstalled into the engine, it needs to be oiled. The oil helps dust to stick to the filter. Place the filter in a plastic bag and add a small amount of engine oil. Knead the oil evenly into the filter with your fingers. Remove the filter from the bag and use a rag to blot the excess oil from the filter. The filter should be lightly coated with oil, not saturated. Reinstall the new or cleaned filter into the air filter base and replace the air filter cover. Inspecting your air filter often and replacing it at least once per year will help to keep your lawnmower running trouble free.

The fuel filter removes debris from your lawnmower’s fuel before they make their way into the carburetor. The fuel filter should be serviced or replaced at least once per year as part of a normal service program to keep your mower running properly. If the filter isn’t serviced regularly it will eventually trap enough debris that the flow of fuel to the carburetor will be greatly restricted or even cut off completely. If your lawnmower starts but then shuts off, you could have a plugged fuel filter. There are two types of fuel filters commonly used on lawnmower engines: in-line and in-tank. The steps to service your fuel filter will vary depending on the type. In-line filters are placed, as the name suggests, somewhere in the middle of the fuel line leading from the fuel tank to the carburetor. This style of filter is usually a canister style filter that is secured to the fuel line with a couple of hose clamps. There are a couple of different types of in-tank filters. One style fits inside the end of the fuel line, where it connects to the fuel tank. The other style of in-tank filter is a metal screen that is permanently attached to the fuel tank. In-line fuel filters should be replaced at least once per year. Start by locating the filter along the fuel line from the tank to the carburetor. Drain the fuel from the tank or use a fuel line clamp to stop the flow of fuel from the tank. Use pliers to release the tension from the hose clamps and slide them up the fuel line away from the fuel filter. Now twist the fuel line to break the seal between the line and the filter. Pull the line off both sides of the fuel filter. Properly dispose of the old filter. Some filters are direction-of-flow-specific, so look for any markings that indicate the direction of fuel flow through the filter and orient the filter correctly. Install the new filter by pressing the fuel lines onto each of the filter’s nipples. Reattach the hose clamps to secure the filter. Permanent in-tank require the tank to be removed from the engine to be serviced. This procedure will vary greatly depending on the design of the engine. In any case, start by draining any fuel from the tank. Once the tank is drained, remove the fuel line from the tank. Next, the tank will need to be removed from the engine. Once the tank is removed, spray carburetor cleaner through the nipple where the hose connects to the tank to back-flush the filter. Also spray carb cleaner through the tank’s fill hole to wash debris out of the tank. Pour the excess carb cleaner and debris from the fuel tank and then reinstall the tank to the engine. Reattach the fuel line to the tank. In-tank fuel filters that attach to the end of the fuel line can be serviced by first draining any fuel that is in the tank. Once the tank is drained, remove the fuel line from the fuel tank. The fuel filter will come out of the tank with the fuel line. The filter can then be pulled out from the inside of fuel line. The filter can be cleaned by spraying carburetor cleaner to back-flush the filter. Once the filter has been cleaned, carefully inspect it for any tears or holes. Replace the filter if you find any. Reinstall the filter into the fuel line and then reinstall the fuel line to the fuel tank.