we await with interest your application of logic and stepwise exclusion of possibilities - it's what we all try to do.

to clarify - resistances and continuities in each coil, and compare the readings between the 2 coils

I tried the Wired george mod to give the coils full voltage and it melted them., 1 after the other. If you have a multimeter compare the resistances and continuities between the 2 coils - you should be able to do this without removing them. 1 of the coils might be on the way out, and reversing the m...

2 inner cylinders - I'm thinking the coil that feeds those 2 cylinders as a starting point to look at. Are you on electronic or points ignition? If points, then the points ( gap, points surface and timing) or the condenser that feeds those 2 cylinders might be the next thing to check

top news, and compression might get even better after its run a bit

put it in a pan of warm water, and bit by bit add boiling water ( not directly on the glass so you don't crack the glass) after a whole kettleful give it 5 mins then take it out ( use pliers) and the metal should have expanded a little

Im not far away, pm me if you want a hand over the next few weeks

presumably the z1000 male and female rear light plug was common across many zeds of the time. Look for the taillight unit from a less desirable bike . Or ask John Browse for his tattiest secondhand one that has a good plug , and use that.

I'd be inclined to charge the battery, refit carbs and exhaust, fresh fuel and get it running. Rev it a few times, (not too hard), and turn off, then let it cool then restart. Get a few heat cycles thru it . Then recheck compressions when its hot , turned over on the starter. The rings might just be...

the threaded section at the top has probably been exposed for decades, so the threads have rusted a bit. Screw it clockwise 3 or 4 turns , to bring the rusty area up then wire brush the upper threads , then screw it out anticlockwise a bit at a time with WD40

as it's the L side, check its not something to do with the speedo drive - it is sitting correctly ie raised part of the speedo casting below and behind the raised part on the fork leg casting to prevent it rotating forward too far? Or are the drive ears on the tubular plate correctly engaged with th...

sounds like a selector fork ( sorry) if it was one of the pawl springs or return spring it might affect all gears

Just a thought. Right at the beginning you wondered about ' incomplete burn" . As I remember, the zephyr 11 has 2 spark plugs per cylinder , and i remember reading in a magazine article that having an extra spark plug in the head was to compensate for poor head design. But if 1 of the spark plu...

Agreed - bit dodgy to oval out the holes to fit, you'll create a weak spot and then one day , on heavy braking ,the calliper will come adrift just when you need it to be rock solid

if it revved ok before the work, its not likely to be the advance/ retard unit