CB400 four misfiring

[smudgediy]

1978 CB400/4 F2
Finished my restoration six weeks ago and bike has been running ok (though a bit rich, can start on half choke!) until last week when it started misfiring on no2 cylinder. Thought it was plug so changed and it ran enough to get me home. Now its doing it again. Changed all plugs to iradium and spark is strong and petrol runs out of drain plug on carb. I'm ok on mechanics but u/s on diagnostics. Any help appreciated.
Des  

Been tinkering, found some loose bolts on cam cover, two overno 2 exhaust. Cannot tighten looks like a helicoil job. Would this cause problem?

[Cleggy]

Have you taken plug caps off in turn and listened for the misfire?
Are you absolutely certain that it is No2 that's misfiring?

Are you also getting a flat spot around 4-5000 revs ?

Assuming that your points and timing are OK, I suggest you check the nylon block behind the side pannel, (battery side).
I had a similar problem and found that it was due to the connectors inside the nylon block that were GREEN.

I have since "bypassed" the block with new connectors individually taped and then taped together, now runs fine.

My problem was the power supply to the coils wasn't regular/good enough.

Like you I also went for a "plug" or HT lead fault.