Thanks a lot guys for all the tips. Today I tested it with a new clutch spring and adjusted the tension to 1.2 mm with 0.5mm end play, it is getting better but not enough yet, will try again tomorrow with different gearing as suggested. I try to explain in detail of my problem. When i punch the throttle to full, the engine roar for a micro second and when the clutch engage, the engine roars lower for about a second or two, there after it started to accelarate faster from mid to top.Compare to my osspeed, it just feel more linear during accelaration. I know this engine supposed to be very quick because I ve seen it during the worlds in Brisbane. I temp the engine it is around 120deg to 125deg. Will changing fuel to 25% helps as well? and will I need to add head shim?