""the max rev I got is 6200 0r 6400 rpm at the full throttle""

tuned for flight I am running my MVVS 35cc at 7200, and my friend is running his DA 50cc at 6500, so I would think you would want to rev a 26cc somewhere around 7400 to 7800 tuned for flight,,


""but nothing change from 60% throttle to 100%""

if an engine's Throttle Linkage is setup correctly you should not feel much of a difference in power from somewhere around 85% to 100%,, so make sure your Throttle Linkage is linear..

Jim