The pilot had expressed an interest in purchasing the ultralight. The owner agreed to allow him to carry out a series of hops along the runway, to familiarize himself with the aircraft. The pilot did one hop and on the second liftoff continued to climb ahead but to a steeper than normal angle. At about 80 feet agl the engine misfired then stopped with the aircraft still nose high. The aircraft turned right, stalled and impacted the ground in a steep nose down attitude. The carburettor main jet was found to be blocked by the remains of an earwig, one of a number that had entered the float bowl via the unfiltered vent ports, possibly while the aircraft was stored in its darkened trailer for the preceding month. The engine failure and stall occurred at a height which did not allow the pilot to recover control before ground impact.