mountfield sp474 cutting out after 4 feet of mowing?

This is the first cut of the year (purchased new less than 1 year ago). After checking the oil and the petrol I started to cut the lawn and after 15 mins motor cut out. Helpdesk said to release the petrol cap and place adjuster at its highest point. The motor started after taking this action, however after 4ft of mowing the motor struggles and the engine cuts out. Any idea how to remedy??