CL72 high rpm issue

[qwerty]

My 1965 250 Scrambler runs great until I the rpms are high. At about 50mph it sort of loses power which comes back when the rpms drop down again. I've gone through the carbs and tried a number of main jets and needle jets without any noticeable improvements and I've put new points in there and am confident that the timing is good. As the work I've done hasn't changed my loss of power, I'm thinking it might be due to valve float and I'm thinking that my next step would be to put new valae springs in it (looks like they're available on ebay as well as gasket sets). Does anyone have any other thoughts? Suggestions?

Thanks,
Graham

[cadman]

What color are the plugs? Are they both the same?

Is timing advancing as rpms rise?

At what rpm?

Are the carbs reasonably well synched?

Fresh gas with no moisture.

Plug heat range?

[qwerty]

NGK D8HS - look pretty good and I've tried it richer and leaner to see if it ran better. The timing is advancing at higher rpms.

[qwerty]

Carbs are synced and the gas is fresh

[cadman]

Okay -

Hot battery - At least 12.5VDC

Maybe coils breaking down at higher rpm -

Air Cleaner restriction? (Plugs would probably be dark)

??????? I just haven't seem much "valve float" problems with early Hondas.

[qwerty]

New battery - just fixed the poorly connected wiring to make sure it's charging. It had one bad coil when I got it which I replaced. Air filters are new. I feel like I've gone through all the "obvious" stuff and the next place that makes sense is the valves. There's about 12000 miles on the bike, which doesn't seem like enough mileage for the springs to be worn out, but then being compressed consistently for 45 years...

[qwerty]

Though it would be pretty easy to try two new coils...