I have a 06 rmz 450 and it is geting hard to kick whay is that

I have a customer expieriancing the same pronblem I would lean to the cam timing or the auto decopresion is worn out from what I can see the part is real loos in the cam and may not be holding as it is passing the shim cup. But first thing check the cam timing as the chain can become very loos due to the manuel screw that gets ignored and the cahin will come loos.

Chances are you need to do a complete tune up. This means a new spark plug, cleaning the carb, new air filter and new piston rings. I would also re-seat the valves. Any further top end work ( replacing valves, bore cylinder and new piston ) is entirely based on what is found after tearing into the head.