Lawn Tractor: Engine Lacks Power

The carburetor blends air and fuel to the right ratio to achieve combustion. Over time, carburetors tend to gum up and may require cleaning. As a part of regular maintenance, you can clean the carb with carburetor cleaner and a soft brush on the inside. Any malfunctioning springs, or missing/weak springs that control the carburetor butterfly valves should be replaced as well. Fortunately, this can be done easily with a pair of pliers, but take note of how they come off, and be sure you do not install them backwards, as this will cause the carburetor to malfunction. After the repair, you may have to set the high idle screw, which can be done by simply turning the screw all the way in, and then backing it off a turn and a half. Then, at full throttle, adjust the screw to where the engine is running properly, which may take a couple of tries to get right, depending on your experience level.

The air filter is located on top of the carburetor of your lawn tractor. 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. This can starve the engine of air and as a result, decrease performance. To clean or replace the air filter, first locate the air filter cover, and remove it. A tab attaches some air filter covers, and depending on your model, it may also be attached by screw. Once the cover is off, simply remove the filter, replace it with a new one, and reassemble.

The job of the fuel filter is to prevent debris and dirt from entering the fuel system and causing clogs. A clog can limit the amount of fuel to the carburetor, causing the air/fuel mixture to be off, resulting in a loss of power. The fuel filter is in the fuel tank, and to replace it you will need a hook to insert into the fuel tank to grab the fuel line. At the end of the line is the filter, which can be pulled off and replaced. With some models, you may have to push the grommet on the side of the tank into the fuel tank before you hook the fuel line.

The gasket is designed to seal two joining pieces together tightly. This will create a seal, and prevent air and fluids from entering areas where they do not belong. A tear or rip in the gasket below the carburetor will pull excess air into the engine, resulting in the wrong air/fuel mixture. This can then cause a loss of power. To inspect and replace the gasket, first remove the air filter and the bolts holding the carburetor down. Once you have access to the gasket, you can check it for damage or leaks. At this point, the gasket will need to be replaced regardless of its condition, as they are designed for one-time use. The other gasket that needs checking for this symptom is the head gasket. The head gasket provides a tight seal between the engine block and cylinder head. If a head gasket fails, it can cause very poor engine performance and it some cases internal damage. To determine if the head gasket is damaged or loose, first make sure the engine is liquid cool, the check for antifreeze leaks around the head gasket. Next you should disconnect and inspect the sparkplugs. A bright or shiny spark plug indicates an internal leak. Check outside of the engine first for an oil leak at the head gasket, then pull the oil dip stick and check for exhaust coming out. Check the vent on the fuel pump and the air filter to see if oil is coming out. A blown head gasket can increase the pressure inside the engine, forcing the oil out in these areas. If you suspect a leaky gasket, it will need to be replaced. To do so, first remove the engine cover and fan, then remove the fuel pump if your engine has one. Next, remove the carburetor and muffler from the cylinder head and pull the valve cover off. If you see more signs of exhaust smoke when removing the cover, it can be another indication of a blown head gasket. Remove all the bolts holding the cylinder head to the engine block, remove the head, and pull off the old head gasket. Then clean both the surfaces of the engine block and cylinder head with a soft brush. You do not want to damage this area as it can prevent a tight seal. At this time, you can install the new gasket and re-assemble. It is best to replace all the cylinder head bolts with new ones as these are usually designed for one-time use. This can help prevent further damage and protect against a second blown gasket. It is important to check your manufacturer’s specifications for the correct sequence of the head bolts, to provide even compression for this gasket. Re-install the carburetor, muffler, valve cover with a new valve cover gasket, fuel pump fan, and cover.

The job of the spark plug is to ignite the air/fuel mixture. A worn, dirty, oily, or improperly gapped spark plug can cause a weak spark. This can result in a misfire or detonation, and a loss of power. Detonation can cause severe internal engine damage as well. Replace the spark plug and gap to the manufacturer’s specifications. Do not over-tighten the spark plug as they can be fragile.

The push rod rides on lobes on the camshaft, and transfers power from a rotary motion to a reciprocating motion. The top of the push rod pushes on the rocker arm, which opens and closes the valves in the cylinder head to allow fuel to enter and exhaust to escape. If a push rod becomes bent, it will affect how much these valves open. If the valves do not open enough, it can result in decreased engine performance. If a push rod is bent, you will usually hear a ticking noise, and if it is bent badly enough or is broken completely, the engine can misfire. To diagnose, remove the engine cover then locate and remove the valve cover. Undo and remove the bolts holding down the rocker arms, and remove the push rods to check for a noticeably bent rod. If the rod is bent, replace it with a new one, adding some engine oil whilst installing. Re-install the rocker arm and bolts to the manufacturer’s specifications, and re-gap to 3-5 thousandths of an inch for the intake and 5-7 thousandths of an inch for the exhaust. Then, replace the valve cover gasket with a new one, and re-install the valve cover.