zxcvbob wrote:

BTW, I buy one 2-gallon can of 91+ octane Premium gasoline in the
spring for the first tank or two of gas in the mower and tiller
(etc.) They seem to start easier that way. When that can is empty,
I switch to Regular for the rest of the season. By then they are
either running good, or they are not going to run good 'til I get
them tuned-up.

87 Octane will start better than 91 (although you probably can't tell the
difference). The higher the Octane, the greater the ignition point.

So-called "premium" gasoline was developed to prevent premature ignition in
high-compression engines.