Yes, take material from the top of the port, and do it a little at a time and keep measuring to make sure you don't go too far and take too much. A good timing figure is usually around 150 to 155 degrees. Using a tuned pipe, you might experiment with a higher exhaust port timing though. Make sure to chamfer the edge of the port so it does not have a sharp edge to damage the piston and/or ring after modifying the port.

AV8TOR