Fuel "grades" only differ in octane, at least nowadays. Just use the lowest octane rating allowed in the manual, if you have it. And depending on altitude (probably a moot point for you fistful), you can go even lower. You can take about one octane point off the minimum per thousand feet of altitude above sea level.
And despite what some people still confusingly think, more octane doesn't give "more power", nor is octane a scam. Some cars/engines need higher octane due to tight timing to prevent pinging/knocking as the higher the octane rating, the "harder" it is to burn and thus less likely to prematurely explode.
Putting in higher octane than is required is a waste of money, and putting in lower octane will either cause knocking (and likely damage over time), or if the car is more modern it will retard performance and fuel economy as the car's computer detects knocking and retards the timing accordingly.
Used to be fuel makers would put better detergents in the higher grades of gas, but I'm not aware of any brands where that is the case any longer. For a little 2-cycle engine (I'm guessing like a weed trimmer?), you'd probably be safe with the lowest grade, especially if the manual doesn't specify anything higher.
