did you try pushing the gas pedal to the floor? Jk. Sounds like you have the same issue that I have. You do realize that the rotax peak power is @ 12400 rpm. I am going to try to get out this weekend or late next week to see if I have my issue resolved. My kart would start to miss and just fall flat on it’s face if I pushed the pedal past 3/4, up to that point it was awsome. I think it is a fuel supply issue so I have rebuilt the pump and replaced all of the fuel and vac. lines. I will let you know if I find anything out.