Recently bought a 1980 Peugeot TSM-U that had been sitting in storage for six years, but just prior was kitted with some fresh goods:
Ported 70cc Gilardoni w/ 49cm Peugeot head
Dellorto PGHB carb
Ninja G3 Pipe
I basically put a fresh bulb in the headlight, air in the tires, gas in the tank, and with a lot of kicking and pedaling got it to fire up. It ran GREAT. Totally ripped. Every time I went to start it after that it was a snap. On its first cross-town ride (5ish miles) it got me all the way there. Then, it sat for about an hour, and refused to start. I had to haul it home and started going down the check list provided by Fred's guide and Myron's mopeds.
Digging in, I learned it had just OK compression, so replaced an old base gasket with a custom CNC machined gasket. Compression was now solid. Took apart the carb and cleaned it thoroughly, so gas flow was very good. I had spark, but it was a bit weak. I didn't think it was so weak that it would be the root cause, and it also didn't make sense to me that this would all of a sudden be the issue. I ignored addressing the spark for about a week, pedaling my ass off trying to get the bike to start. Got lucky once but otherwise couldn't replicate.
Then I pulled the flywheel off and discovered the magneto wiring was being chaffed through by the edge of the flywheel!
The white wire was almost completely severed, clinging to itself by two strands. Reattached that sucker and wound it with some heavy rubber and electrical tape to keep that from happening again. Spark was now definitely stronger.
Reset timing to 1.4mm BTDC (was previously in that same ballpark) and tried to start the bike—still no luck.
Then I checked plug gap and set at .4mm, and checked and set the point gap to .4mm (was previously .3mm, and points were already clean).
THE TSM NOW STARTS ITSELF. Like Cheetahchrome's 103, the bike is a runaway.
Time to dive into tuning!