No Compression!

My good friend from CT came for an extended visit (unemployed again) here in sunny SW Florida a few months ago, and he just happened to have a 2001 xr650 in the back of the truck
It wasn't running to good and difficult to start, so I went through the fuel sys. and uncorked the pig. Started 1 kick every time and ran great.
My friend left and I convinced him to leave the bike behind. YESSSSSS!
Just recently I went out for a spin, the motor started to "run away" like it was sucking air and fuel WFO! yet the throttle was closed. I had to use the kill switch for what seemed like forever to shut it down.
Now it has no compression.
I think a leakdown test is where I should start, but does anyone have any experiance with what I described or a good idea what happened?
Thanks

Carb, plus the cables (1 loose or broken) - fix all that first, it got stuck, and you don't want a repeat.
Then, before you take the top off, take off the decomp cable, at the head!, and make sure that lever moves back - still no compression?
Then take the top off, and if I were you I'd take the jug off too.