Small Engines (Lawn Mowers, etc.): Ryobi 42 Riding Mower Wont Start, compression release, hp engine

Question
This Ryobi mower with 17.5 HP engine will not start.  I have replaced the starter, battery, solenoid and batter cables.  It used to kind of drag and then start, after the new parts, but now just makes a click noise at the solenoid.  Could it be the switch?  That is about the only thing that hasn't been replaced.  This mower doesn't have alot of hours, but starting has almost always been an issue. Thanks

Answer
  Rapid clicking means a weak or loose connection, one solid click
means the solenoid is clicking/working, recheck and make sure
it is hooked up to the starter correctly.  Cable from the battery
to one of the big posts on the solenoid, the other big post, the other cable to the starter.
  In general, your hard cranking symptom is usually because the valves need adjustment, because the compression release is not being allowed to work.

  If you could find some model numbers off of the mower and the engine, I could be more precise in telling you what to do.
There are a few good vids on youtube on adjusting valves, you might
look at some of them.

Thanks
   Fish