Boyer Mk3 to Boyer Mk4?

... done the same with my Electra, which had a Mk3 box when it arrived. I've just replaced that witha Mk 4 box for the very same reasons - although haven't yet tried to start it. So I can't give you anything but encouragement! The Boyer Bransden people are very helpful.

Yes, the MKIV is much improved, as detailed on their site - much more friendly now for electric start bikes!

It is not the MKIII at fault, it's just a limitation of the tech/design of a unit that's been around for nearly 40 years.
 

Don't be tempted to change just the transistor box - change the stator plate too.

Wiring diagram here:
https://granttiller.com/norton-commando-wiring-diagram-boyer

BB said that it would be fine to use the original. I have of course improved the way the leads attach, partly by junking the horrible pre-insulated crimps.

@ian age takes it's toll, and the cables/connectors/soldered joints become less reliable over the years.

Plus, the strain relief is very slightly improved on the later NT1a stator plates.

Sounds like you have answered your own question by making improvements to yours already!

We have had the MK 3 Boyer on an Atlas for many years .and the battery has not been alwaysup to snuff. However we have not experienced kickbacks at all. Perhaps its because we have a fat blue cap fitted .