When left for lengths of time...the oil drains away from the cylinder wall...which in turn causes lose of compression.....these engines use a splash method to lubricate.....it can take some effort to get them going again when left for long periods without being started. Iv had to go through it a few times now myself with the eu20i. I simply apply a small amount of fuel/oil mix to the spark plug hole, and slowly pull on the starter rope to oil up the cylinder wall.
Always use the more expensive petrol..high octane as it will burn better and you get a much better tank to run time ratio. If leaving for any length of time..try to drain the carby as the additives in the fuels will caramelize and block the jets....PITA.
I hate to disagree narrawa but how can oil below the rings affect compression, and using higher octane fuel is also a myth, use the recommended fuel only, draining the carby is a good idea as you are correct on this point, if storing for a long time i would recommend removing all the fuel