Motorcycle Repair: Honda CB200T 76 with at speed bucking, plug caps, flat surfaces

Question
Bill,
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
Check your spark plug caps, be sure that the plug heat range is correct.

Remove the point plate and inspect the spark advancer for proper advance/return action. Reset the initial timing to the F mark.

Check the carb syncronization so that both slides are raising at the same time. Be sure that both float levels are set correctly... 21mm

Be sure that the carb slides are not reversed. There are different ones for left and right sides.... if you swap them, all kinds of interesting things happen.

Check the petcock for clean fuel flow through the ports and that the petcock filter is clean.

Bill Silver