Yeah, it might be slightly different fuel from country to country Per, here in Oz we got rid of leaded fuel in the early 2000's which really messed with older cars and bikes, back before then we only had "Standard" (around 92 RON) and "Super" (around 95 RON) so when we went to unleaded most older bikes ran fine on 91 RON unleaded, some ran OK on 95 RON unleaded, and most ran like sh1t on 98-100 RON unleaded.
I was running 100 RON unleaded in my 1993 BMW K1100LT and it loved it, but my CB750F2 with brand new OEM points plate and coils/plug caps didn't like it at all, just like has been said above, it ran really rich. I'd replaced them because I had a real problem with the bike when I first bought it that whenever I rode in the rain (even in just a wet mist) the bike would run like sh1t, but in the end it turned out that the F2's ignition key switch was faulty. Anyway, I bought a new old stock Dyna III from a member here (Mike Beltrami) back in the Greenspun days, and it produced a fat blue spark, so I tried some Shell Optimax (98 RON) with the Dyna, and it ran as well as the BMW! Seriously, there was virtually no cranking, I'd just press the button and it would fire right up, and just ran better right thru the rev range.
From that I surmised, that the weaker spark from the points ignition wasn't effectively igniting the fuel/air mix. I've seen a similar thing happen on my first Suzuki GS1000S that had the factory electronic ignition and worked fine with a fully charged battery, but the alternator's stator was stuffed so it couldn't keep up with the power requirements of the bike on a long ride, and as the battery got flatter, the engine seemed to run richer, something almost impossible on a bike with CV carbs and stock jetting.
I've got another Dyna III that I bought from another US member (Chewbacca) recently that I'll install in my K2 "Bitsa"so hopefully it'll be as good as the one in my old F2, and if so, with 125 mains and pods filters, it should run pretty well for a stocker! Cheers, Terry.