Spark on 3 cylinders

[Graemesig]

Having just acquired my all time dream bike - a 79 Z, it's not really going so well
I bought the bike in Holland, and have just brought it home to the UK. The bike is close to perfect condition with only 950 miles from new. It has lived most of it's life in someone's living room.
Before I bought it, it was commissioned by the Six Centre in Holland, with carbs set up, fluids changed etc. I hear they know what they are doing, so felt confident. When I viewed it 4 weeks ago in Holland, it ran like a dream. Now back in the UK, it will only run on 3 cylinders.
Using a heat gun, I established that cylinders 2,5,6 are working, cylinders 1,3,4 are not. I suspected the dreaded CBX gummed up carb issue, but checking the plugs established that 2,5,6 have a good spark. 1,3,4 have no spark.
So it's an ignition problem. But how can this be when 1 and 6 share a common ignition circuit? I could understand it if it was just a problem on 3 and 4, which also share a common circuit.
As a first step, I would be grateful for any advice about what to do next.
As a second step, is there someone to recommend that can help? I am accustomed to working on bikes, but have no experience with CBX's. I'll try a few things myself, but after that would prefer to enlist the help of a specialist. I am in Leamington Spa in the Midlands.
Thanks for any advice,
Graeme

[daves79x]

Try all new plugs first. Bikes that have been run very little, and not warmed up and run out well, often have fouled plugs, even if they look OK.

Dave

[Graemesig]

Off to try that now.....

[Graemesig]

Dave, I am very grateful
I rejected the plugs on the basis that they looked fine, and 3 can't go down at the same time.
New plugs now fitted, and the bike purrs like a kitten.
Thanks,
Graeme

[Larry Zimmer]

Happy endings. Enjoy, Graeme. And, welcome to the cult!

[steve murdoch icoa #5322]

Nicely done, Dave.

[hondaman160mph]

One more thing I have learned from Dave's knowledge and experience, priceless.

[wyly]

that's surprising to find "three" dead plugs after Bert at sixcenter had it running without the same problem...