Motorcycle Repair: 1974 CB 750, electrical faults, internal shorts

Question
Hi Chris,
The story on this bike is so bloody long that I'm not sure where to begin.  However, I'll try to keep this as brief as possible.  
My first day out with the bike it began back-firing terribly out of the right pipe. It seemed to be running on two cylinders.  The right pipe turned red hot and it simply quit.  
The shop replaced the needles in the carbs, fuel lines, filters, put in an electronic ignition, replaced the coil for 3-4.
The bike however continues to run fine for a day or so and then I experience periods of power loss where I seem to loose two cyliners.  It becomes "boggy" and tends to back fire. Sometimes it passes and the power returns and other times it powers out all together and quits. It cools for a bit and then fires up again.  It seems to come and go like a seizure. The first time  cylinders 3-4 cut out and the last time it was 1-2.
I can't figure out if this is electrical or fuel related.
Any suggestion will be be hugely appreciated.
Thank you kindly,
George  

Answer
Hi George.
 There are two probable causes here.  One, which is least likely, is valve/ignition timing and the other would be intermittent electrical faults (1 or more) in the ignition system.

 To fix or check these problems you will need the repair manual as it has all of the specs, proceedures and wiring diagrams that you need to find the problem.

 The most likely problem is an electrical fault in the ignition system.  I would start looking for it/them in the wires from the coils backward to power.  Look for points where the wires could arc or ground to the metal of the engine and/or frame, bad connections, or where the insulation may have worn or melted away.  Then check each line from each coil with a multimeter for internal shorts.

 As old as that bike is, if the wiring is original, then it may, likely, need to be worked on.

Let me know how it goes.
Good luck.
FALCON