Stihl recommends 89 octane, or higher, gasoline for their equipment.
I was purchasing a new Stihl KM 130 R KombiMotor trimmer the other day, (it cuts heavy grass almost as well as my very old 4-cycle Ryobi 1079r ... but that's another story!) and the salesman was very persistent that I know to purchase 89 or higher octane gasoline for its use. I thought this was because of the "4-cycle" X-Mix engine used on that particular trimmer .... but later, looking back thru their catalogue I see high octane gasoline is recommend for all current equipment.
On the page listing all the Stihl mix oils, there is this note: STIHL recommends a mix of 50:1 high-quality 89 octane or higher unleaded gasoline to STIHL engine oil. This same mix ratio should be used during break-in.
When did this come about? I've been asleep at the switch if it applies to my older Stihl equipment. I've been using 87 octane regular non-leaded.
Heads up!
There's a lot of debate about that. One argument is that high test has less alcohol...I don't know but I burn high test alcohol free gas in all my small engines and I have very few problems.
I also believe that at higher altitudes you can burn the lower octane. Less air density, less chance for detonation.