[cyrusb]

I hate to be "that guy" but it is often overlooked and is potentially an engine killer.
 I am talking about the cotter pin that keeps your decompressor valve out of your cylinder.
 I was shocked when I discovered mine was halfway through at ten years old.
 The cotter pin is soft by nature so it can be bent easily and maybe not the best choice for this application.
  Replacement is easy by pushing out the old one with the new one so its never without a pin in it.
  Or you can take it out. Or you can T.D.C the cylinder and rope it. Either way it pays to give it a look.

[Karl Childers]

They are small and frail, last time I had mine apart it was not reusable and I didn't have another one at hand. I'm not big on using bent nails in place of cotter pins but I had some brads that were the perfect size  and much sturdier than the cotter pin it replaced.