Small Engines (Lawn Mowers, etc.): spark test, air filter element, crankcase pressure

Question
how do i check if i am getting spark on my briggs and stratton 17.5 hp john deer riding mower.  i am burning up lots of oil and my plug keeps on gumming up with what looks like oil blowback, and now i cant get it to fire up even with a new plug, do i have a blown ring, piston . the mower is 5 years old and used to pull multiple loads of heavy rock and a heavy roller.

Answer
If the engine is operating you have spark but to answer your question remove the spark plugs put them back into the spark plug boot and prop them up against the cylinder head.  Turned key as if to start the engine and observe spark at the gap on the spark plug.

If proper maintenance was not done to the engine there could be where in the cylinder, piston or rings.  This maintenance would be changing the oil at proper intervals and maintaining clean air filter element.  The most likely situation is positive crankcase pressure.  This is caused by an air leak in the crankcase the most likely spots are the oil filled to and the dipstick O rings.  There could also be a leak at the crankcase sump.  Another area would be the engine crankcase breather.  This is best identified by a small rubber to that would go from the air cleaner assembly to the breather.  The purpose of the breather is to vent crankcase pressure.  If it is full of oil you could try cleaning it but the best thing to do would be to replace it along with the gasket.  Oil could be pushed into the cylinder past the valves stems normally there would have to be many hours on the engine.

The other thing would be an overflowing carburetor.  This would be evident if gas is in the oil.  If this is the case you would notice your oil level rising.  To repair this a carburetor kit would be install including a new needle valve and seat.  Hopefully this information has helped.  Be sure to replace the gummed up spark plugs.