O.S. GT33 Petrol w/E-5030 Sil.The second engine in the latest O. S. GT series of petrol engines is designed for the new class of models that are emerging onto the market that are specifically targeted at this size and type of engine. Many of these models are sleek in design, so O. S. has chosen a rear mounted Walbro carburettor with reed valve induction. The advantage of spark ignition petrol engines over regular glow engines is the optimised ignition timing across the rev range