I inherited a never-run MS170 and an unopened gallon of Motomix last year. The unadjustable-carb saw ran really rich on the Motomix, contrary to what I’ve read here about most of them running borderline too lean. It blubbered like a MX bike trying to race with the choke left on: pretty much unusable. But it didn’t smell bad; I thought it smelled kind of like race gas exhaust.
The saw ran, and continues to run, much better on my normal 32:1 premix I use in my other OPE.
My new Redmax strato trimmer loved the Motomix though, and also smelled like race gas exhaust and emitted no visible smoke. The trimmer also runs well on the 32:1, but smokes a little on cold startup.
Recently I tried Stihl HP Ultra at 32:1 and it doesn’t smell exactly like the Motomix did, but vaguely similar. I think the Motomix smell comes from a combination of the fuel and the oil in it.
EDIT: for some reason I got censored for trying to abbreviate Outdoor Power Equipment...?