Honda-SOHC

My 78 400f2 model seems to have a charging system problem and I can’t get to the bottom of it. I had a series of problems in which the battery was unable to start the bike after or during a run and also appeared totally dead at home one morning when it had been fine the day before. A multimeter showed 12.4, 12.5V at the battery when the engine was running regardless of the revs. It should be 14.5 to 15V when revving to 3000 and beyond according to Haynes.
- Subsequently I put in a new battery but after one check when it was charging correctly at about 14.5V at 3000 revs, it reverted a few days later to 12.4V, or 12.2V with the headlight on
- the multimeter showed the rectifier was ok as was the generator.
- Unable to check the regulator so I replaced it and the old rectifier today with a combined regulator/rectifier from David Silver. But the problem remains with the battery only being charged at 12.4V
- the only other oddity is that the electrics twice were completely dead (no ignition lights when I switched on).The fuses appear ok. I prised apart the ignition switch connector and cleaned it with a brass brush, and everything came back on again.
Any ideas gratefully received

Hi to everyone. Just acquired a 78 CB400 F2 with a believed genuine 15,000 miles on the clock. Rode it 100 miles home, sadly far too much on the intimidating M25. Seems to run well apart from a slight hesitation when opening the throttle from a steady speed, and tending to cut out when changing down at slow speed. Any ideas? Has had a recent carb strip and clean apparently. I have just fitted new air filter and plug caps but no difference. Used to have an identical candy antares red F2 in the late 70s (VLP267S, where are you now?) which took me on an epic 5,500 mile tour of Europe in 1979, so the new bike is a bit of a trip down memory lane…