Hey guys I'm in need of you're vast knowledge. I have an 84 xr500r (in my service manual it shows mainly the same engine as the 600) and the last time i went riding it started smoking. It has smoked on start up since i have owned the bike ( i figured it has worn valve seals) and while going downhill but it will block out the sun when i as soon as i touch the throttle. It hasn't lost any power but used a half quart of oil in the two hours that i was out. What gives? Is this a common problem with air cooled engines? I'm guessing that i have worn the rings out and it's time for a new piston and rings but i would like to know if there are other things to check first. I have checked to make sure that the vent is clear.