If you have a look inside the petrol cap it states that the minimum RON to be used - 98.
Up until recently my local petrol station had Super unleaded which was only 97 RON, so i've always used normal unleaded - 95 RON. Its a bit split on here really as to which is better. Technically the higher the RON rating then the better the fuel will burn.
However, i've tried 95, 97 and the more recent 99 RON fuel and to be perfectly honest I didn't notice any difference (apart from the price!!!). Similar MPG and power.
Mine is a digifant which is an electronic injection and apparently advances and retards the spark according to the fuel you use. Yours is a K-jet and will not advance and retard as it is a mechanical injection. If the guy said use the super unleaded then I assume its set up for that fuel. You could try normal and see what happens??