Lawn Tractor: Engine Will Idle But Dies At Full Throttle

The carburetor mixes the air/fuel together to the proper mix for combustion. Locate the carburetor underneath the air filter, remove air cleaner cap, and look for any obstructions in the way that could block air flow, starving the engine of oxygen. Next, check for any adjustment screws. Sometimes simply adjusting your carburetor’s settings will solve this problem. To adjust your settings, first locate both idle screws on the carburetor, one will be marked L (low) and one marked H (high). Turn both screws inward to shut off the flow of fuel, then turn the screws back in the opposite direction 2 turns. Next, start the engine and let it idle for 5 minutes. Turn the L screw clockwise to add more fuel as you set the idle. Next, at full throttle turn the H screw clockwise to set the high idle. Continue to adjust the screws until you have the engine running at peak performance. This process will require some experience and may take some adjustments before you get it right.

The air filter is located on top of the carburetor. Its main function is to allow clean-flowing air into the engine and prevent small particles from damaging internal engine parts. Over time the air filter will need to be replaced as it becomes clogged with small particles and debris, starving the engine of air and power. This can result in the engine stalling at full power. To inspect and/or replace the air filter, first locate the air filter cover, and remove it. Depending on your model, the cover may be attached by screws or just a tab. Once the cover is off, remove the filter, replace it with a new one, and re-assemble. The air filter should be cleaned and replaced as necessary, as part of regular maintenance.

The fuel filter is located between the fuel tank and the carburetor and prevents debris from entering the carburetor and engine, causing damage. A partially clogged filter can starve the engine of fuel at full throttle, which can cause it to die. You can check the fuel filter by gently twisting the fuel line off both ends and blowing through it. If it is blocked or you suspect it is partially blocked, then you will need to replace it. Checking and replacing the fuel filter should be a part of routine lawn tractor maintenance.

The gasket’s job is to create a seal that prevents air and fluids from entering the wrong areas. A damaged gasket below the carburetor will pull excess air into the engine, causing the air/fuel mixture to be wrong. This can cause the engine to die when you run the tractor at full power. To check the gasket, start by removing the air filter and loosening the carburetor bolts. Once it is visible you can check the condition of the gasket; look for tears or rips or any indications of leaks. The gasket will need to be replaced at this time regardless of condition, as they can only be used once.

The spark plug is designed to ignite the air/fuel mixture in the combustion chamber under any condition. A damaged spark plug, or one that isn’t firing properly, can cause the engine to die at full power. To check the spark plug, first remove the wire from the spark plug. Be careful doing so as the plug can be fragile. Next, remove the spark plug and check its condition. Sometimes a good cleaning and re-gapping to the manufacturer’s specifications can solve this problem. If the engine runs at high RPM a lot of the time and/or under heavy load, you may require a cooler-running plug to dissipate heat quickly.

The push rod transfers power from a rotary motion to a reciprocating motion in your lawn tractor. The top of the push rod pushes on the rocker arm, which opens and closes the valves in the cylinder head. This allows fuel to enter and exhaust to escape. If a push rod becomes bent, it will affect how much these valves open. If the valves don’t open enough, they can restrict the flow of the air/fuel mixture and exhaust, which can cause poor engine performance. If a push rod is bent you will usually hear a ticking noise. To diagnose this issue, first remove the engine cover, locate the valve cover and remove it. Undo the bolts holding down the rocker arms and remove them, making sure you remember where they came from. Now you can remove the push rods and check for a bent rod, which should be noticeable. If the rod is bent, replace it with a new one, making sure to add some engine oil to them before installing. Re-install the rocker arm bolts to the manufacturer’s specifications, and replace the valve cover gasket with a new one. Make sure to clean the surfaces of the cylinder head and valve cover, before you re-install the valve cover.

The boot on the spark plug wire is designed to house the connection that the spark plug snaps into. Over time, the boot can crack, causing a ground-out issue, or they can simply come apart. If they are old and cracked you can simply pull or cut the end of the boot off. When purchasing a replacement boot, make sure to get the inside connector. Next, push the long end of the connector into the side of the wire and try to center it for the best connection. The connector should slide in easily, but you still may need to use a pair of pliers to ensure the connection is snug. Next, spray a small amount of lubricant into the boot and push the connector in. Finally, re-install the boot onto the spark plug.

The purpose of the fuel lines is to deliver fuel from the fuel tank to the carburetor where it is mixed with air for combustion. If the lines are clogged, the engine can become starved of fuel, and this can cause it to die at full power. To inspect the lines, first pull the fuel line off the carburetor gently in a twisting motion and do the same on the fuel tank and fuel filter. Be careful when disconnecting the lines as fuel may start pouring out, however this is a good indicator that your lines are in good condition, and fuel is flowing normally. At this point, you should also blow through the lines looking for anything unusual coming out. If you feel a restriction when you blow through a line you have a partial blockage, and the lines will need to be cleaned or replaced. Lines should also be replaced if they look old or cracked, as they can leak and cause a fire.