Small Engines (Lawn Mowers, etc.): Too much compression?, automatic compression release, compression stroke

Question
I have a briggs 14.5 I/C motor off my tractor, The engine ran fine until one day it wouldn't start. It will crank over with no problem when the spark plug is out of the cylinder. When I put the plug in the cylinder and go to crank it over, it goes 3 cycles and stops on the 4th cycle, like it has too much compression.
Is it possible the engine has carbon build up on the piston or the valves are out of alignment?  

Answer
These engines normally build up an excessive amount of compression, and doing so, they are equipped with an automatic compression release(ACR). If the valves are out of adjustment by as little as .008 it can make the engine impossible to turn over with the normal size battery a mower calls for. You will need to remove the plug, rotate the engine to tdc on the compression stroke, and check the valves. Most of the briggs engines call for .004 intake and .006 exhaust. I hope this fixes it for you, if not you could have a broken ACR.