Hi i have a gamefisher 7.5 hp. it is from 1982. It overheats really quickly. this engine is air cooled so i cannot figure why it would overheat. I have the oil/gas ratio correct and the heat sink on the engine looks to be clear of obstruction. It always starts right up, but it then begins to overheat and from there it begins to lose power. what could cause an air cooled engine such as mine to overheat. any suggestions would be appreciated!!!