Small Engines (Lawn Mowers, etc.): B&S motor, old briggs, cast iron engine

Question
Matt,

  I have an old Briggs 300421 12hp cast iron engine that has spark and gas, but refuses to start.  Can you tell me how to check and time this engine?

Answer
If you dont suspect the carb is fouled and you know it has spark then it sounds like a compression problem. this can be due to the cylinder wall scored or a valve is not sealing or stuck open start with a compression gauge check. after a few turns of the motor you should have around 80-90 psi if its low, its cylinder wall or valve not sealing if there is no compression whatsoever probably valve stuck open which happens cause of varnish/gum build up around the valve stem. it could be timing but i've never worked on this type of engine. if it was timing you probably at least be getting a backfire out the muffler or the carb.