Motorcycle Repair: Honda CB200T 76 with at speed bucking, flat surfaces, gas cap

Question
Chris,
I'll try to be as clear as possible.  The above bike has about 4k mi on it and runs well generally.  My current problem happens at speeds of 55-65 mph and 6-7k rpm and happens 80% of the time predictably.  At this speed on flat surfaces with engine warmed up, the bike starts bucking as if one cylinder was not firing.  Slowing down for some time (45mph or so) can resolve the problem temporarily.  The plugs are new as are the points.  I cleaned the carbs myself with soaking.  Seals are good.  My thoughts are centered on the fuel system or possibly the timing (which is slightly advanced).  The fuel lines are new.  Opening the gas cap at speed doesn't resolve the problem but may help somewhat.  The choke has no helpful effect.  Have you experienced this type of problem or do you have any ideas?  
Thanks in advance,
Martin
PS I have had rides at speed with no problems what so ever.

Answer
Hi Martin.
 The bucking is related to fuel flow.  The fact that it is clearing up after lower rpm runs is indicative of this.

There could be a couple of things causing this here.

The carbs could be out of synch, badly.  Or the carbs could (and probably do) need a thorough and proper cleaning.

Just soaking the carbs will not clean them out correctly.  They need to be disassembled and cleaned properly.

Start there and let me know what you get.
Good luck.
FALCON