Motorcycle Repair: 1981 Kawasaki KZ750 ltd H inline 4 losing cylinders, kawasaki kz750, kawasaki kz 750

Question
Hi,  
I have been having trouble trying to figure out what is wrong with my Kawasaki KZ 750 LTD H inline four motrcycle.  Ive gone through the Cltmer manual time and time again trouble shooting the electrical, but still no progress.  The problem is that when I try and start the bike it used to fire right up, but after 5 mins of running it would drop cyclinders 1 and 4.  then 2 and 3 would follow shortly after.  Once dead I cant get it to fire again.  Spark plugs are new, I installed another set of coils but the problem still followed to a T.  Now I can only get cyl. 3 to fire.  Carbs are clean, and the cyls. are getting fuel.  I can only think that it is the CDI ignitor.  Please Help if you can,   I love this bike it was my fathers and I want to continue riding and enjoying it.

Answer
The CDI Ignitor may be the problem, but first you may want to check for pinched wires, as this is a common problem. I would also get a digital multimeter, as they are not expensive, and check if you have voltage on all the wires with the kill switch and the key on(assuming it has a battery). Check for loose wires, anything common, then if none of this works, it is most likely the CDI ignitor.