Guess what the problem is?

Hey George...if it is the coils and you can hang on till after Christmas I will have a set of good stock coils you can have cheap. I am upgrading to Dyna greens, but have to wait to Christmas to get my paws on them. They are currently under much wrapping paper, transparent tape, and bows!

If coils are leaking juice the 'view in the dark' is a good idea. If they've been doing it a while, the dirt tends to pattern on them which is a good clue to avoid when buying used.

Suspect one might find a marginal spring with shim removal tool and a good sense of feel. Sure you could find a broken one that way Easier than pulling head.

-Duck

Not sure one bad spring would cause the cut-out at 7K rpm. If it were valve springs, would be more than one... probably all of them are weak. I have a spare head that I could put on, if needed, but will look at the coils first... BTW: The Accel coils are not cracked nor is there any special amount of dirt on them. I checked resistance (primary/secondary) a couple months ago and probably will actually look at the problem tomorrow.

UPDATE!

Finished up some work yesterday, then tore down a set of carbs and put them in the tank to soak... THEN I WENT OUT AND LOOKED AT THE PROBLEM BIKE...

I put the carburetors I finished testing on the bike with the problem to ensure that the problem was still there. It again cut out right at 7K rpm with a different set of carburetors. I also changed my almost new Autolite fuel filter out for another in the event I had a bad filter. It happens... Problem was still there... Bike pulled like a freight train up to 7K rpm and them it felt as if there was a rev limited on the bike...

I decided to try swapping coils. I pulled the Accel coils off and put on my spare set of Dyna coils. I scruffed up the areas that were cracked and applied a coating of JB Weld over the cracks first. I initially had spark in 2 & 3 but not 1 & 4! Since the coils had worked when I took them off, I again removed them and tested primary and secondary impedence and they checked fine. This time, I swapped the coils from side to side and tested them again. This time, the problem was fixed and the bike would pull redline easily. I can't figure out why 1 & 4 would not fire initially since I undid the connections and reconnected them but I obviously had a bad connection first time around.

The Dyna coils show about 3.8 ohms primary and about 13K ohms secondary impedence. The Accel coils should the same primary but about 11 K ohms secondary. I suspect that I will try the Accel coils again at some point thinking there may be a bad connection but they may just have an intermittent short.

a simple problem is always satisfying

it's those darn pull the head drop the pan split the case tofind the problem and then scrounge a month for parts that drive me crazy...

-Duck

I am putting a new spare engine together and have most any part needed if I found an engine problem. I hope to get that darn spare engine together this weekend if the weather cooperates as I don't like to work inside in the shop on engines. I am going to pop it into one of my test bikes and then split the cases on that bike and swap out transmissions. Not having second gear aint so bad but it sometimes is balky going into 3rd and higher gears... that can be really annoying! Cheers and thanks to all who chimed in! It made me think hard whether I measured the valve spring lengths on the head that is in this bike... I still can't recall for sure hehe

I know this is redundent, but did you try another set of carbs on the bad engine?, I still find it hard to have a problem just pop up from nowhere, with no other signs first.
one last thought, what about the plugs, what did they look like , I know a short run is going to be hard to read, but I think it would show a bad cyl even with the poss. bad valve spring