Small Engines (Lawn Mowers, etc.): kohler ch18 blowing compression through the intake, automatic compression release, blown head gaskets

Question
my kohler ch18 just started missing today and popping through carb.  pulled carb and burst of air comes from right cylinder back through the intake.  checked compression on the cylinder and got 115psi. got 125psi on the other cylinder. i dont know where to go have checked the flywheel key. thought it could be head gasket or cracked head wanted to have a second opinion before tearing it apart. thanks

Answer
The service manual link is below:

http://www.kohlerengines.com/onlinecatalog/pdf/tp_2428_b.pdf

I would start by removing the valve cover and checking the valve system.  

If you have access to a leak down tester you can quickly verify a cracked head or head gasket.  Cracked heads are rare as well blown head gaskets.  However, I have found a few head bolts that vibrated loose and caused the head gasket to leak.

Compression Test
Some of these engines are equipped with an automatic compression release (ACR) mechanism. Because of the ACR mechanism, it is difficult to obtain an accurate compression reading. As an alternative, perform a cylinder leakdown test.

Don't forget the easy stuff, especially the spark plugs.  I have had brand new spark plug, right of the package, fail.  I would replace the spark plugs before tearing into the engine.

Let me know if the link helps.
Eric