Re: Scratches in the bore
Generally, anything that you can do to smooth the ports, inlet and exhaust, and remove rough castings restricting flow is a good thing, and can increase the power by about 5%.
The fuel mixture is used for more than fuel, it also cools the top of the piston, and lean air/fuel mixtures are harmful.
Usually, grinding material from the ports and increasing compression will add power but it will leave flat spots in the RPM range. Otherwise, it may have good peak power, but have mediocre mid or low end power. To me, it's irritating to have flat spots in the power band.
It seems that to get the greatest satisfaction from engine modifications requires going all the way. That means increasing compression, changing port timing, optimizing timing and ignition, improving and enlarging the carburetor, and fitting an expansion chamber designed for the rpm range that the engine will be operated in. Often, the engine improvements will increase the peak power and the upper RPM range.