Small Engines (Lawn Mowers, etc.): john deere 425 wont run, john deere lawn tractor, john deere lawn

Question
I have a 1995 425 John Deere Lawn tractor with a v twin liquid cool john deere k series 20 ohb engine.  It has got gas and spark. The fly wheel turns but the motor sounds different and will not start.  I believe it is in the front end of the motor such as the timing chain.  What do you think is wrong with it?

Thanks,
Jason  

Answer
MY first question on this matter is how long has the unit been sitting up. By the way you explained it, it sounds as if the intake valves my be stuck open from varnish build up of old fuel. This is a rather detailed job to go into. Run a compression test on the engine to see if the valves are in good working order. I usually like to see around 140 out of these engines on each side. If your compression is low, remove the valve covers and inspect the operation of the valves. If the valves are sticking, it will require the removal of the head or heads to resolve this issue.

Hope this leads in the right direction.

John