what gasoline to use for 50:1 - 87, 89 or 91

i was wondering what gas i should use to set up my mix

87, 89 or 91 ?

any ideas?

I have an old outboard. The only thing i do is add sea-foam or star-tron to every tank of gas and i changed out all my old gas lines with the new ones that aren't susceptible to the new junk gas . I use 87. i used to use 91 on my other boats but it is not needed.

u leave the engine run w/o gas line to empty the carbourator when u leave the lake ?

Naw, Sea foam stabilizes gas for 1 yr. best stuff on market!
I summarize my auger with sea foam and a full tank of gas every year and it starts and runs mint all the time. I use sea-foam on any engine that gas might last longer than 30 days in tank. Lawn mower,generator,weed whacker, ice auger ect.