After looking into this mechanism, both in the XR600R's manual and while holding it in my hand, I've come to a conclusion: What the heck is going on here? Check out the description written by Honda: First page Second page I've used my best brain cells, or those that are left anyway, in figuring out how this thing works and I can't understand one thing: They say that the spring that sits inside the decompressor cam (item 2 in the lower left drawing on page 1) is responsible for opening the right exhaust valve below 800 RPM. How so? Calling this spring "weak" is an understatement... How in the world could a spring this lame open the exhaust valve with its stiff spring? Anyone?