I just finished restoring a 1971 CB750 and had sputtering when I gave it full throttle. I removed the air cleaner to troubleshoot and the problem did not occur. So that told me it was running too rich at full throttle. At full throttle, the main jet is the one to change, so I went from a 120 to a 112.5 and it now runs great throughout the rpm range. Once you decide if it is too rich or too lean, you need to figure which jet needs to be changed. If it occurs at all ranges, I would lower or raise the needle jet as appropriate. If you need to make it richer, raise the needle and if you need to make it leaner, lower the needle. Take a look at the plugs and that can help troubleshoot too. I don't think your .5 over on the pistons will make any difference with the jetting.