hi ive got what i think is 1972 mercury 650 thunderbolt engine because it is a four cyl and not a 3 cyl.i looked at merc outboards.com and tried to cross the serial number to verify my thoughts but i couldnt find the number listed,if anyone can help it would be greatly appreciated--ser #1890932 and it says keikhaefer mercury again it is a 4 cyl 65 hp,i think