Fitted 'Racing Reed Valves' - Loss Of Performance

[Snek]

Hi. I was hoping that someone out there could help me with a problem I am having. I fitted some 'Racing Reed Valves' to my Benelli K2 100cc 2T. It has a Minarelli engine (Stock), the same one that's used in the Yamaha Aerox 100cc I believe. Anyway, I fitted these for the first time ever, and it has actuly decreased my performance. I've lost a little acceleration, and lost 10mph on top end. I fitted them exactly as the stock ones came out. The only thing I did not do is fit a new gasket, as the stock one looked fine. The reeds I installed where 6 valve ones, while the stock where 4 valve ones. The power-band or power-range isn't as harsh anymore, it seems to be holding back. I even tried lighter rollers and a spare new-ish belt that I had lying around, no improvements. Any ideas people? :(

So far my mods are;
Exhaust System
Open Air Filter
Re-Jetted
Racing Variator
Lighter Rollers
2000 RPM Clutch Springs