You may of collected a little moisture in the float bowl. You might drain it and start fresh. In this area, we have a hell of a time with ethanol blended fuel and anything with a carburetor. Some of the country store gas stations are trying to sell straight gasoline because of problems with property maintenance equipment doing the same thing your's is doing under a load. I'm not looking forward to what we will be dealing with for fuel in the next few years. Carburetors are going the way of rotary dial telephones and home delivered milk.
I don't think it is octane related. I believe it is the additives that are used to slow down the separation of gas from alcohol, the alcohol's tendency to attract moisture, and the reality that today's gasoline has a shelf life about equal to a jug of milk.
“many a trip continues long after movement in time and space have ceased”- Steinbeck, [I]"Travels with Charlie"
[FONT="Century Gothic"][I]Sometimes your only available transportation is a leap of faith[/I] [/FONT]