Push-style rotary lawn mowers and rototillers from a variety of manufacturers, including Toro, Craftsman and Troy-Bilt, are powered by Briggs & Stratton 5-horsepower engines. Like all small engines, this one requires regular maintenance, or it can develop performance problems. When your lawn mower or rototiller won't start or stalls while you're using it, the problem is usually fairly easy to solve, requiring maintenance of the spark plugs, air and fuel filters and the carburetor.
You can trace many performance issues to lack of fuel or no fuel at all. If you can't start your lawn mower or rototiller, take a look in the fuel tank -- you may have forgotten to add fuel. If the tank has fuel, consider how long it has been there -- old fuel collects moisture and can gum up the carburetor. If you're starting your machine for the first time this season, it's best to use fresh fuel. Use pure gasoline -- the manufacturer does not recommend methanol fuel. You should also check the fuel filter and replace it if it looks dirty or worn. Consult your owner's manual for the location of the filter -- your engine may not have one.
Restore Air Flow
If your lawn mower has been running rough and has now begun to stall, it may be because you've neglected to clean the air filter. Access it by unscrewing the air filter cover on the top of the engine. When you remove it, you may also have to remove a pre-filter; you can clean the pre-filter with soapy water and tap the filter cartridge gently on a work bench to remove grime. If they are dirty enough to cause stalling, however, you should probably replace them. Add a little oil to a clean pre-filter, squeezing out the excess. In addition to the air filter, you should also clean the spark arrestor screen located behind the muffler, if your engine has one; check the manual if you aren't sure.
Check and Clean the Spark Plug
If your engine has been operating on bad fuel or with insufficient air, combustion is incomplete, and carbon deposits have probably collected on the spark plug. Pull the boot off the plug, unscrew it with a spark plug wrench and clean deposits from the spark plug terminals with sandpaper or a file. Check the gap between the spark plug terminals with a gapping gauge and adjust the gap with pliers to be 0.03 inch. Replace the plug if it's overly fouled or the terminals have eroded. To keep your engine running smoothly, you should check your plug after 25 service hours and replace it if necessary. You can also drain old oil at this time and add 21 ounces of new oil.
Adjust the Carburetor
Several hours of running your lawn mower or rototiller over rough terrain can throw the carburetor idle adjustment screw off, which can cause the engine to stall when you release the throttle. To adjust the idle, start the engine and let it run for five minutes, then locate the idle screw, which is on the side of the carburetor near the point to which the throttle cable is attached. Set the tool's throttle lever to low, then hold the throttle cable lever steady while you turn the idle screw to adjust the idle speed. Turn it clockwise or counterclockwise as needed, and adjust it just far enough to get the engine running smoothly.