Firstly, I know it's not a Ford, but is a lot of knowledge on here, hopefully covering old carb'd French shitbox's

Old 205 XS 1400, randomly backfires, could be once a mile, or not for 20 miles.
Had my toe down for a long time earlier, and it cut out.
When it cuts out or backfires, the rev counter stops working.
When power comes back, rev counter works.
Has had everything on spark side renewed, other than ignition amplifier - I'm sure it's an amplifier, coil is a module more than coil I'm familiar with.
I've adjusted the timing.

It seemed as if it was running out of petrol, but the backfires would suggest lack of spark, and fuel wouldn't effect the rev counter.
Seems as if heat is the issue - the times we broke down it would be ok after a few minutes.

Anyone any ideas? Got me stumped.
Think need to know where the rev counter feed is, not as simple as I'm used to, a green wire by itself or similar.