At first I thought old mercs answer was a little vague....then I looked at the serial number charts. Your number is above the range for an 88 115 hp and above the range for a 150 hp. Its not a 90. The carbs may be the only way to tell for sure. Look for the WMK number on the fuel bowl of the carb. For example if its a WMK 14 its an older 150 (like old merc has).