Hi,
You did lose a little on the exhust and transfers. My 25cc is 100 degree transfers. 150 degrees exhust. 132 degrees intake. You can cut a 45 degree shanfer around the piston 1/2 mm deep. This will give you back your timing without loseing the compression gain. When I cut ports I use masking tape to protect the cylinder walls where I don't want to cut. It is not a matter of if you slip, but when you slip.

Dave