Open the head to 45mm and cut 7-12° from the angle of the piston crown so the gasses are forced to the center of the head. Stock closed chamber (higher compression) head has a issue with spark plug being very shrouded, so you want to dress the bumps that deflect the flow, and also unshroud the spark plug, so the fresh charge can fill where you want to have the flame kernel start right at the spark plug.
Run the ignition at 1,5mm BTDC (or 1,2mm if you have CDI) to get the heat of the combustion down the pipe and still have the piston take a lot of the power from the expansion.