What is that light flashing near the plug; Is it intentional?
No ideas?
Think it's what is called an 'éclateur' round here GB. A spark-gap introduced into the HT lead. I've seen them on quite a few bikes, especially Motobécanes, over the years.
Some say - and we've been here before on this one! - that these things intensify the spark at the plug. I think they are dubious at best. Some say you can't start a Citroën 2CV of a damp winter's morning without introducing a secondary gap - like the old 'button' thing - and there must be evidence to support that or it wouldn't be done quite widely . . . But I am a sceptic.
As to the funny exhaust noise, I reckon Richard is right. Am I not wrong in thinking that radical valve timing can create a somewhat similar effect? I remember being amazed watching Tractor Pulling competitions in rural New England 30+ years back, where several blown V8s were stacked on extraordinary chassis. Those engines on deceleration made some incredible sounds as unburnt hi-octane (nitrous oxide more than likely thrown in even) went off bang all over the place. The least tame bits of machinery I ever saw!