Thanks Bruce and Victa Man
I have now removed the plastic bits from the screws - the settings as delivered by Bunnings were - low: 1.5 turns off seat, and high: 4.5 turns off seat.
Have now tried to start it, on the new settings, and nothing. Except a fine pair of blisters on my fingers. Tried to start on original settings - will run briefly on full choke but dies. Removed plug and blown it with compressed air. Nothing. Clearly has spark.
Although about 5 years old, this machine has been run, from new, for less than 30 minutes, never been wet etc. (I bought it new).
Not impressed. Once I cool down - it is warm and humid here today, I shall go to work.
Any further tips?