Motorcycle Repair: 91 honda nighthawk cb750 - no spark, honda nighthawk, plug caps

Question
I have an intermittent problem with spark on the bike.  Sometimes the bike runs smoothly but sometimes I'll loose power and it sputters.  I can usually get it to run again by unplugging and plugging the spark plug boot.  When the bike is sputtering I can unplug the spark plug boot and don't even feel a difference, so I'm reasonably sure that the problem is I'm not getting spark.

I just rebuilt the carbs and I'm pretty sure they are operating well.  

I measured the resistance of the the boots to be 4.5-4.9Kohm.  The primary coil and secondary coil resistance checks out (3ohm and 13Kohm respectively) and I checked the wiring harness to the ignition control module and have connectivity there too.  

I thought it would be the plug wires or the coils, but it seems like the resistance values are within spec.  Is 5k the expected resistance of the plug boot for this bike?  

I just want to get this bike reliable - Please Help!!!

Answer
Mark, which spark plug boot are you disconnecting? Plug caps are generally in the 5k ohm range, so I don't see anything out of line there.

http://www.bikebandit.com/houseofmotorcycles/honda-motorcycle-cb750sc-nighthawk-...
for parts illustrations.

If the whole thing cuts out and quits, I was leaning towards the pulser coil going out of range or having loose connections. If you are pulling one plug cap loose and it improves OR doesn't change, you are disconnecting BOTH cylinders, as the coils are double ended and service 1-4 and 2-3 cylinders respectively. BOTH coils have to be attached to grounded spark plugs or at least grounded to the engine, in order to complete the secondary circuit.

Check your carburetor diaphragms for any pinholes. Looks like you have a vacuum operated petcock and the diaphragms in those are known to fail. Check the vacuum line to the carb and pinch it off momentarily to see if the engine responds. When the diaphragm fails, the engine gets a vacuum leak on that cylinder and the fuel flow is greatly reduced.

When you pull a plug cap loose, like that, the voltage spikes up and helps to clear a fouled spark plug. Make sure that the plugs are good and not cracked on the insulator.

Bill Silver