Just like the title, how often do you have to change the oil and adjust the valves? Is there other maintenance that has to be done and whats the frequency between rides? (the internet yields only differences in the riding experience, not real world issues) I have a 250 EXC and I'm thinking of upgrading to a KX 450 or a 450 SX/XC. All I do now is keep it clean and greased, change gear lube and mix gas. What am I looking to get myself into?