If you had bought a Peugeot moped out of the newspaper, and picked it up out of a residential garage 20 years ago, you could probably of ridden it home from there and never had an issue with getting good spark at the plug.
Skip ahead 20 years and now that foolproof ignition coil is 40 some years old and the insulation properties of its design are starting to crack and fail. The bike develops symptoms of hard to start and wont idle.
You then find an OEM brand new coil on the interwebs and hooray, the bike performs like new for a week then the symptoms reappear. Turns out that NOS coil you paid for is new, yes, but older than the one you tossed away. So you might be having starting conditions where it might start easily when cold but then once warm its hard to start.
If when trying to start you have to pedal like crazy on the kickstand only to have the motor suddenly snap to life as if a switch had been thrown. you could have a leaky coil. If the bike will run but if you slowly twist the throttle down to approach a
respectable RPM to idle, the bike cuts off, again as if a switch has been thrown, this too can be a leaky coil.
A leaking coil is when the charge built up in the coils winding takes a short cut out of the side of the insulated parts of the copper winding and jumps to the nearest metal or grounding point so that it never completes its journey through the plug wire to the spark plug. When the bike is hot the air between the coil and the stator plate metal is hot, and that hot air creates an ideal condition for the spark to take the short jump to the ground of the metal, thus robbing the spark from the spark plug. This is why the bike might start ok when cold then get all finicky when hot. Sometimes conditions have to be just right.
To look for evidence of leaking coil you can remove the nuts from the ignition coil mounting studs then slide the coil off so you can see the backside. The back of the coil sits very close to the stator plate so if your coil is leaking it will certainly arc to the closest grounding point. The black spot in the yellow circle pictured above is the tell tale evidence of the electric charge has been arcing through the side of this coil and taking the easy shortcut to the stator plate.
In this close up shot you can see a crack in the insulation. A person might be able to buy some more life out this doomed coil perhaps by coating the outside of the windings with some sort of goop or nonconductive spooge.
There are several aftermarket replacement coils available that I have had good luck with that bolt right in but in all cases you need to build a new plug wire and boot. Also in all replacements you will loose your brake light connection as the replacements all only have a single wire for the points only. You ultimately have to swap out your brakelight switches for non grounding types and leach power from you head/taillight feed.
There is another homemade method taught to me by Graham Motzing (http://www.mopedarmy.com/riders/mobyman/) where you rebuild the ignition coil by totally stripping off all the old winding and building a single strand type primary winding that you then use with any external cheapo Hi tension frame mount secondary coil. It is a lot of work but it was very gratifying to build a coil from scratch that produces a fat blue spark. Here is a link to his method, http://outofcontrolmopeds.blogspot.com/2011/01/peugeot-103-ignition-coil-re-winding.html
The best cheapest way to upgrade your points system woes are to chuck them totally and up grade to a CDI system. I always use this La Partie CDI for Motobecane. It bolts right up with just a adapter and some longer stator plate screws. You will still have to trade out your brake light switches and leach power from the headlight circuit but this unit makes plenty of power for all. https://www.treatland.tv/motobecane-CDI-p/motobecane-cdi-ignition.htm
If you have any questions about the CDI I suggested, or are having trouble with the install contact Cheetahchrome http://www.mopedarmy.com/forums/profile.php?6,26847