A glaringly obvious fix would be to arrange a rear brake. However we knew we had no inner cable. So we moved onto the chains.
Being an autocycle, i.e. precursor to the moped, it has pedals. Being as there is no kickstarter, these are used initially to propel the machine, and thus turn over the engine until it bursts into life after which they are redundant except as places to rest your feet.
Well that's the theory. In practice the happy commuter of yesteryear may well have used them to 'speed' himself up hills and other inclines if he was eager to get home to his tea before it got cold or eaten by the Cat.
The mechanical upshot is that there are two chains to the rear wheel. One is exactly like on a bicycle - connecting pedals to rear wheel. The second is from rear wheel to the gearbox. All very well except that adjusting the tension of one chain will affect the tension of the other one. It's a bit of a laugh.
Anyway the designer had taken this into account - the pedals are mounted on an eccentric which can be rotated to take up slack and we found that if we took one link out of the drive chain then we could take up the generated slack in the pedal chain by rotating the eccentric. Got that?
The upshot was nicely adjusted chains, right up to the point where one ancient spring clip snaps.
Bother, (see above)