I had some fun today.
During a test ride my right leg suddenly got really hot; looking down I see it is covered with oil; pulled up to the barn and shut it down; took a look; hmmm, the end cap on the right side of the head, right where the camshaft is, was gone !
Thinking back to when I put it together I think I must have put it in backwards.  First time I have ever done that, I must have been REALLY sidetracked when doing that.

This quick test ride is getting very long.

I don't believe it would make a difference which way it was installed (other than appearance).  The shape of the plug is nearly the same with it installed either way, and it should have stayed put regardless of which way it was installed.

The only other person on this forum that has blown that plug out is the genius that decided to just cap off his breather pipe....the engine had no place to vent.

If you blew out the cam plug - you must have had some serious pressure building up inside the engine.

Check your screen in the head and make sure it is not all gummed up, and that your vent hose is clear.  Maybe the filter you have at the end of the vent hose is too restrictive.