Motorcycle Repair: 1975 CB360T, spark plug gap, cylinder pressures

Question
Rich,
   I believe I have a carburetor problem.  The bike starts easily and idles fine.  When I get up on the road and my RPM's are above 4000 or so I'll suddenly loose power and then get it back again.  It doesn't seem dependent on throttle position.  I sealed the tank this winter and put new fuel lines and inline filters on.  I rebuilt the carbs, new jets etc so I'm pretty confident its clean.  Any hint as to where I should start to look?  At first I thought I might have a timing problem or a ground in the ignition system but wouldn't something like that show up at idle?

Answer
Michael, I was going to say it sounds like it's running out of fuel but I don't understand why you would recover just as suddenly.  

Start by checking fuel flow to the carbs.

It could be a plugged fuel filter or the vent in the tank cap is partially plugged. You can check the vent by leaving the cap loose and see if it doesn't fix the problem. You can also pull each of the hoses off the carbs and let them run into a container to make sure there's plenty of flow going into the carbs.  If the flow is okay, the restriction could be inside the carbs and something is restricting the flow into carbs.

If the carbs are getting plenty of fuel, it's probably an ignition problem.  It could be a plug wire or coil breaking down.  The coils could be getting hot and shorting out internally or when you are under load they could be breaking down.  When the cylinder pressures increase, it takes more voltage to jump the spark plug gap.  If there a weak spot in the coil or plug wire or if the plug gap is too wide, the spark will find another path to ground that has lower resistance like through the plug wire to the engine block.