1988 Yamaha XV1100 virago (Athlone_Ireland)

[OwenVMurphy]

Looking for some help. I bought a 1988 Virago 1100 last week. 30k miles, full service history. Carbs cleaned, full service, new battery before I collected her.
Starts absolutely on the button, cold or warm. Runs and idles lovely.
After driving for approximately 10 miles, bike splutters, looses power, drops revs, picks up again, drops again (sounds like it's down to 1 cylinder), no power when you hit the throttle. I have had it out in wet and dry conditions over the last few days and no difference. It seems that the bike will still run if kept at 50 mph/ 3,000rpm. If left to cool for a while it will go back to running well for a short while.
My experience with outbound motors would have me thinking ignition coil. Any opinions from ye that know these bikes better than me.
Thanks in advance from Ireland.