still sounds like the carbs the valves wouldnt effect it. possible theres a air leak somwhere in your engine causing it to run like that i have had the same problem and was due to a crack in my crankcases that only seamed to let air in at full revs
_________________
Honda nc23 CBR400 AERO 1986, 1990 honda NC23 Tri-Arm, 1987VFR400 NC24 Rothmans Rep, NSR250 MC16 1987, CL250s 1983. Moto guzzi zigolo 110cc 1958. Fantic 50cc 1972. Suzuki Cobra Race bike 500cc 2t 1975 , GP125 1975. Triumph T110 1954. BSA Thunderbird 1955. Ariel VB 600 1952, 1990 MuZ 125 etz.