CB750kz not firing on No 2&3 cylinders

[Mike the Bike]

Hello good people!
I have a 1979 750kz that is refusing to fire on No 2 & 3 cylinders.
I have recently overhauled the carbs and had them sonically cleaned.
I have renewed the coil and swapped them over with each other and still no joy.
I have put new HT leads on.
I have swapped the spark units over with the same result.
There is still no spark at the plugs, can anyone enlighten me on what the problem could be and where to look next.
Many thanks
Mike

[CB750Winger]

  Mike, this might be a long shot but I recently put new NGK plugs in my 75 CB750K and it started running on 3 cylinders right away. #1 plug was dead. I switched new and old plug back and forth 3 or 4 times and the new plug was bad. Try checking the plugs and switch them around.

[Mike the Bike]

Thanks for that, but I have already swapped the plugs around and they are all good.

[woodsrider250-2]

Maybe one of the ignitors?  There are two....One for 1/4, one for 2/3....These fire the same time respectively...

[Mike the Bike]

What do the ignitors look like and where are they situated?

[oldbayman]

I have an 82 cb750f and they are 2 square units under the seat on mine.

[woodsrider250-2]

Yup....Sorry, didn't see your reply to my post.

[Mike the Bike]

I assume by igniters you are referring to the "spark units" as they are described in my manual. They are the two little silver blocks with what looks like a black plasticy tar like substance in the backs of them. If it is these you are referring to then they have been swapped over and shown to be working ok.

[liljohnnie69-2]

might be a pickup,have you removed the left side ignition cover and checked the pickup sensors? or maybe you have a corrosion problem in an electrical connector somewhere.

[woodsrider250-2]

Hmmmmm, could be one of the crank pickups.