Small Engines (Lawn Mowers, etc.): How to set timing, compression stroke, valve clearance

Question
I have a Honda GC190 the numbers on the block is GCAAA-1090115 QHAF. How do I set the timing? It use to be very easy to start but now it will jerk the rope out of my hand. I'm thinking that it has jumped timing. Please help.
         
         Thanks, Jason

Answer
Is the enigne still together?   If so, leave it together.  Is there gas in the oil?  Can you pull the string with the spark plug removed?

Start by checking the valve clearance.  Valve specs on page 10:

http://engines.honda.com/pdf/manuals/00X31Z8A0230.pdf

To check the valve clearance all you need to do is remove the valve cover and set the engine at top-dead-center on the compression stroke.  Watch the video starting at 2 min 54 seconds.

The video link below covers lapping valves.  You DO NOT need to remove all the parts just to check the valves.

http://www.youtube.com/watch?v=XJJ3G6xKChk&feature=related

http://www.youtube.com/watch?v=v0BCvemfKvo

http://www.lawnsite.com/showthread.php?t=291763

Take a look at the link above and let me know what the valve clearance is.

Eric