Briggs & Stratton makes gasoline engines for many brands of lawn mower. Like all engines, they require regular maintenance and may at times encounter problems. Most problems with Briggs & Stratton lawn mower engines can be solved by a homeowner with a little troubleshooting; major problems may require a professional mechanic.
If a Briggs & Stratton lawn mower engine starts and then stalls immediately, the first thing to check is the air filter. Most engines use some type of foam filter, usually just above the carburetor and held in place with a long screw. Remove the screw, take the filter out and examine it. If it is dirty and clogged with oil and dust, wash it in warm soapy water, let it air dry thoroughly and then replace it. If it won't wash clean, replace it.
Check the fuel if the air filter is good. Gasoline will go bad quickly in a mower tank. If it has been a while since you bought or added fresh fuel, drain the gas tank by turning the mower up over a large container and refill the mower tank with fresh gasoline, newly purchased, not from the same storage container. Put the old gasoline in your truck or car; it will be diluted enough there not to matter.
Clean the carburetor next. Remove the air filter again and spray the carburetor with a commercial automotive carburetor cleaner. Spray inside the carburetor and the outside links, too, to remove any dirt or debris that might be causing them to not move properly. Spray a bit of starter fluid into the carburetor if it still starts and dies; sometimes a tiny clog just needs to burn out to restore operation.
Remove the spark plug and make sure it is good. Disconnect the plug wire and take the plug out with a wrench. If the plug is burned or fouled with oil and carbon, replace it. Make sure the plug wire is good and solidly connected; a loose or shorted plug wire can cause an engine to stop.
Call a Pro
Take the engine to a professional repairman if none of these steps solves the problem. It is possible a diaphragm inside the carburetor has worn out or been damaged and may need to be replaced. Don't try to rebuild the carburetor yourself unless you are an experienced small engine mechanic.