Run 89 in that motor as recommended in the manual and keep it stabilized (even during the season unless you are burning through a tank every two weeks). You could siphon off the gas and use it in cars or lawn equipment or you could add some 93 back to whatever is left of the 87.
2 parts 87 to 1 part 93 = 89.
Previous: 1993 Prostar 205
Red 1998 Ski Nautique, PCM GT40, 310 hp, , Acme 4 blade, Perfect Pass SG/Zbox.
Be kind. Have fun.