or has it developed a magic rev limiter situation?
This situation can happen and is usually caused by:-
A duff pickup coil (which will show as ok with a resistance check
) You need an oscilloscope to see if these are working properly or not.An excessively worn mag bearing.
Twisted crank webs.
Intermittent continuity of the LT coil:-
This is a notorious fault that is well discussed on this forum. To test for this:- connect a multimeter set on the 200V+AC range across the green wire connection and ground (moving coil meters are preferred to digital here but not essential).
Start engine and get it warmed up good: At tick over expect a reading of 60-75v which should rise to around 200v as you rev it out. If the reading flattens out early then this is typical of a failed LT coil.
These poorly connected LT coils suffer badly from engine vibration and temperature changes resulting in a fractured earth tail wire which only connects when the vibration and coil temperature is low enough. It's this intermittent connection of a bit of copper wire, about the diameter of a hair, that causes the rev limitation. A lot fail within the first 100 miles.
It's an easy test to do..... for peace of mind if now't else.
Good luck.
