I have an 84CR500 that has been nothing but a big pain in the butt. I got it knowing it needed the engine to be rebuilt (low compression) so I did that. I found in the rebuild that the head was leaking so I had it milled just enough to smooth it out and had the cylinder bored. I also replaced the piston and rings naturally. Once I got the thing together the compression felt good, but it ran horribly. I tinkered with the main jet and the timing (which I shouldn't have touched) and got it running better but it still ran like crap. It would either bog on the low end or high end. Well, after a few hours of riding it (basically all just test rides after the changes) the engine lost a ton of compression and would barely run. I checked it and there is only 41 lbs of pressure (how much should it have anyway). I took it apart and the rings are flat on one side and the plug is in bad condition (I thought the piston had melted due to the plug condition but it didn't). What went wrong? Now I need to do this all again and I want to make sure this time it works!!!