One more thing, on my 88 RM250, there is a rod that comes up to the head where the exhaust valves sit from the actuator (right side of engine). This rod pushes up a arm, that rolls a bar counter-clockwise (which goes through the tops of the valves and closes them), which connects by a spring. This spring HAS to be on properly or else the valves will not work well and will stick open (which is their origional position. The spring has 2 arms that come down and surround two small ends of levers, which allow them to move freely, but keeps them together unless there is alot of force in opposite directions. This spring is very often put on wrong, with the arms crossed, when the arms must be straight for proper operation. Do you have the book and follow it exactly when you put the valve train back together? I'm not sure how much the design has changed from 88 to 99, but its most likely the same general idea. I hope you can see what I'm trying to explain, its fairly difficult on paper without a drawing. Also, check the left side of the engine where the tensioner sits. Make sure everything is ok there. Good luck.