1977 900ss Bevel misfire


I have a 900ss (1977) that I have rebuilt over (a considerable) number of years.
I have just got it running (this month) but have a problem.

The bike has a new (alloy) tank, taps, tubage and I rebuilt the carbs using new jets, floats, accelerator pumps etc. But the bike has a misfire at high revs… at about 3500 rpm. I checked the plugs. The rear cylinder is a nice honey colour but the front cylinder plug is black. I cleaned both a tried again, but same thing.

I checked the carbs, but everything looks OK. I swapped the coils over and plugs around (but kept the HT leads on the same cylinders as their lengths mean they can’t be swapped. Still the front plug seems to go black and I getsome soot out out of the RH silencer when I rev it

I do not think it is carburation as it ticks over like a swiss watch and goes on full throttle without missing a beat. It’s just at around 3000-4000 rpm.

I’m going to replace the HT leads, plug caps and fit a pair of new NGK BP7HS plugs. Any other suggestions anyone?

Have you replaced the ignition pickups?