-Pulse-Jet Ignition is a revolutionary new way of igniting the main cylinder charge, by igniting a small charge in a confined space the pressure and temperature rise very quickly, the emerging explosion from the PJI ports ignites all areas of the main combustion far more efficiently than the heat from a single spark, the differing port volumes of the insert creates an internal low pressure after the initial explosion, drawing in any unburnt fuel and air, as in a Pulse-Jet and fires again and again...around two hundred times per second.------------------------ Please note that for twin spark models the Pulse Jet ignition in only fitted to the upper plugs---------- • Marked increase in performance and in low rev pick-up • Quicker throttle response • Smoother engine operation • Lower fuel consumption ==== Only spark plug requires changing for service. PJI will not need replacing.