Still waiting for the shop manual..... It just goes to show you that it has been awhile since I have worked on a bike...1999 WR 400. Just to think that to change the spark plug you have to remove the tank...and there it is...just under the main frame tube...and 2-3 inches below the top of the head....Do you use a Yamaha socket to remove it? Got it out with an "elbow" joint socket...yet afraid of not getting the threads right when I replace it...AAAHHH the good old days...when the carb was simple, the plug right there, the air filter simple to get to...no radiators and comfortable to sit....When are they going to come out with a revised XR600?....UUUUPPPPssss this is a Yamaha forum:> One more mystery...removed bolt on bottom of case to empty oil from engine...about a quart and 1/2 came out....yet with the bolt still out I just happened to take a reading from the dip stick and it indicated over full??? Could there be a vacuum created where the rest of the oil doesn't flow or is there a second exit to empty the oil???