You can raise the exhaust port a half a millimeter with the top of it flat for 12 or 14 mm with radius in the corners of the top and or shorten your header 1/2 inch.
My friends who race go karts and have put them on the dyno have found that Peak power happens on air-cooled cylinders at 418 degrees Fahrenheit with the reading taken at the base of the spark plug with a thermal coupler.