Dellorto pilot jets for the Dellorto 19-21 mm PHBG - PHBD carburettors. The pilot jet is responsible for controlling the fuel mixture at lower revs. If the incorrect size is used, this can lead to problems. Pilot jets that are too small will make the engine cut out at lower revs. In some circumstances the idle can become hard to adjust, as the engine tends to rev too high and then suddenly cut out. If the pilot jets are too big, the engine will splutter and not pick up well at lower revs, as it is running too rich. Various pilot jet sizes are available. The size of the pilot jet is generally stamped on the jet itself and can be read once removed. In your delivery, you will receive a correctly corresponding pilot jet.