If it was originally brown it would be a 1963 model. If it was always yellow then it would be a 1964 model. Those foil serial number decals are a pain. They used them through 1966 then switched to a riveted on serial number tag. The 7 & 8 hp units used a 224XXXXX serial number range from the first unit in 1962 through the 1966 model year. 10 hp units used a 286XXXX serial number range. Starting in 1967 they switched over to an 820XXX model number on the tag which was the dealer order number also. In my opinion most of the value is in the condition of the foil serial number tag. You have a nice example of a 63/4 model that many collectors would love to have. I don't have one in my collection.