I have a 1978 TS 250 and it stopped running. I have spark, and fuel, but no compression. Any ideas before I start tearing it apart?

 

have you checked under valve cover ? is the chain still connected? do valves still move up and down? have you taken plug out put finger in hole and kicked it? could be a couple of things relief valve could be stuck, or chain can be broke, or just rings wore out , i would try looking under valve cover first that will tell the tell . I know yeah duh but try the simplest first i don,t know if your mechanically inclined but try it and see . Hope i could help.