I have a 1991 Honda CR250. I just had to pull the top-end yesterday because it has a fresh rebuild and the person that put it back together didnt do it right and bent the cam spindle and rack for the power-valves. They werent working at all. While I have it apart I was thinking of milling the head. How much should I take off if I use 93 octane gas? Will I notice a differance? It was rebuilt using a sleeve. I dont like those but it looks to be a good job and was running good before except the power valves didnt work. Thanks. Jim.