Make sure the piston is set at Top Dead Center on the compression stroke, too. Click HERE for a better understanding about the shape of the intake runner port. When grinding the ports, feel each port for smoothness. Because any roughness will disrupt the atomization of the fuel with the air, causing loss of power. In fact, all engines built nowadays or since unleaded gas was first introduced have hardened exhaust valve seats.
Valves are unaffected by unleaded gas.
Also, unleaded gas helps to keep the combustion chamber free of carbon deposit buildup. Boil liquids together. Pour in dry ingredients and stir together. Knead and add flour as needed.