stock, these guys are hard to destroy, imho.
because it did not seize, tick off the following list of things to check / replace:
1. did you run out of gas. im not being a silly goose, appropriate gas flow helps a gurtner.
2. clean carb. that air filter crack could suck in particles and gunk that might clog small holes. or shit from the tank, but gurties have a tickler anyways.
3. spark plug - make sure it didn't suck in a grain of sand that got wedged in the spark plug gap. this can cause erratic misfiring and junk.
4. condenser/timing - get a new one. also get a micrometer timing tool or digital calipers and check/set the timing.
5. ditch the 2 coil for a 5 coil altogether, and put an external (or at least new ) condenser. the wiki prolly has some kind of information on this stuff, but try searching here or lmk if you need a good 5-coil diagram.
6. compression - test it with a tester! check ring condition, replace if necessary, check cylinder/piston for wear.
you should be able to do all this on the bench and get it back to life. the non variated ones have a shorter drive-side crank and maybe different cases (?) no clue.
if you are on the fence, give this lil pug a fighting chance ;)
please post a pic of the frame too if you can!