As Matt said you do not need anything more than 87 but the crap they call gas goes bad so fast I'm running VP SEF 94 or 112 race gas when I have some leftover from my racecar. Yes it's expensive but it keeps the carb nice and clean. I also use SeaFoam in all my small engines.
http://www.vpracingfuels.com/sef-94.html