I know this might be in the wrong section but its prolly okay. This problem is on my 1981 KZ305. Im sure the mechanical speedometer is the same principal as the VN750. My speedo seems to be reading about 25-30% slower than actual. when it says 30mph, it feels like 40 or 45 on my vulcan. and the odometer seems to be running slow to, leading me to believe that the head is not the problem. what else could it be? a wrong gear? wrong tire size? thanks.