I don't have any idea what the problem might be.........but I do have a thought.........
Sounds to me like it might have jumped time? Is this possible? Is it possible to land hard enough, if the chain has some slack, for the timing chain to jump a cog or 2??
I think the valve clearance can spec but if the timing is off a little could create the symptoms that you describe....
Disclaimer: since I know nothing about 4t mx bikes......if this isn't possible or the rmz doesn't have a timing chain then please disreagrd my thought on the grounds of ignorance...ha