Here is what worked best for me:
Engine Acceleration Lvl.3
Clutch Boost Lvl.3
Chassis Flexible Lvl.3
Suspension Stiff Lvl.3
Traction Grip Lvl.3
Brakes Hard Lvl.3

I use this tune on 250 and 450 4 strokes, but it might work good on 2 strokes aswell.