Why won't your Briggs stratton start?

That's a tough question as there can be many of reasons WHY a small engine such as a Briggs & Stratton wont start. The usual problem on most small engine's such as this is a dirty carburetor meaning the fuel jets in the carburetor are clogged. Eaither that or if it is a diaphragm type carburetor, the diaphragm which acts as a fuel pump on small engine's gets hard because gasoline, expecially todays gasoline with the harsh E-10 and alcohol additives, eventually dry's this out to nothing short of the similar stiffness of cardboard, thus no longer can pump fuel. That is only one reason why a small engine wont start but 90% of the time, it is carburetor trouble.

Another symptom can be a bad spark plug, a bad ignition condencer (engine dating pre-1985) causing a weak spark or in the case of an electronic ignition engine, (newer than 1985) a bad ignition coil.

If you have hit something hard and/or the engine has taken an immidiate shock and died, you may also have a sheared flywheel key which will throw ignition timing off thus creating a "no start" situation. All above symptoms are easily repaired though if you are mechanically, somewhat mechanically inclined or even a fast learner.

How about dirty fuel? I am trying to get my daughter's lawn mower running with a 6.5 HP B&S engine. She didn't run the engine dry last year and there was a combination of varnishy gas, water and gum in the float bowl.

After cleaning everything up, it would start, but not run and then quit starting. I removed the spark plug and it still smells like varnish so I will drain the tank anew and put in new fuel.

Next step is to drain the tank anew and replace with clean fuel.