FUEL INJECTED SCOOTERS – AN INSIGHT
There are two main options to deliver petrol into a scooter engine… carburettor or fuel injection. The former of which has been the preferred choice for two-stroke scooters with very few exceptions. During the 60s and 70s, Wal Phillips fuel injectors were available as aftermarket kits for motorcycles and scooters. By today’s computerised fuel injection system standards, the Wal Phillips was crude by comparison. While the scooter press at the time were complimentary about Wal Phillips injectors on scooters, in reality, the reaction to the practicalities of using them was mixed at best. When used on a scooter for sprinting, the Wal Phillips fuel injector was successfully implemented by legendary names including Arthur Francis, Fred Willingham and Frank Osgerby to name but a few. The Mk1 version Wal Phillips injector was not easy to set up. How they ran depended on many factors, including how much fuel was in the petrol tank! For everyday use on the road, as much when de-throttling as accelerating, often the former led to the engine flooding, followed by inevitable problematic attempts to get the scooter to restart. From personal experience of riding an SX225 with a Mk1 Wal Phillips fitted, it started well from cold. Accelerating through the gears it was impressive, however, decelerating for a road junction ahead the scooter coughed, spluttered and then drowned. There is an excellent guide to setting up a (Mk1), Wal Phillips fuel injector on a Lambretta which was published in Scooter World magazine in 1966. Walter Phillips himself was present at Brands Hatch press day for the dealer special PJ Oakley demonstration. The former world speedway champion turned engineer did a few runs on the PJ Oakley demonstrator fitted with one of his, Wal Phillips, injectors, without any flooding problems. Though Wal, being the design engineer, obvious had correctly set up the fuel injector on that Lambretta. The Mk2 Wal Phillips injector also known as a Jetstream was launched in the late 70s. In contrast to its predecessor, which had an adjustable linkage and a butterfly valve fitted to a short metal tube, Jetstream fuel injector had jets similar to those used on carburettors. More consistent power and performance was available at that time from aftermarket larger choke size carburettors.
One production scooter to have fuel injection as standard was Aprilia’s SR50, launched in 1992. A model that has sold over 800,000 units, the fuel injected engine was jointly developed by Australian Orbital Corporation and Siemens AG. Orbital Corporation, under the name Dy-Tech, continued developing fuel injected two-stroke engines throughout the 90s. Scootering magazine ran several features on their development in the late 90s. Many manufacturers of two-stroke motorcycles have for many years had fuel injected two-stroke engines way beyond the development stage. There are several manufacturers offering bolt-on fuel injection kits for two-stroke engined two-wheelers currently on the market, although there's been little if any reported use of any of these kits being fitted to scooters. Yet right up until last year,
when both Husqvarna and KTM announced their intent to launch motorcycles with two-stroke fuel injected engines, for sporting use, nothing else has gone into commercial production. Probably, this has a lot to do with the EU intention to bring in a pan European ban on two-stroke engines, using emissions legislation among other things. This will still apply in post-Brexit Britain, whether the political divorce is hard or soft. The advent of totally electric scooters in the near future may well have implications for new four-stroke scooters of the future too.
Honda introduced the first fuel injection system on a production two-wheeled machine in 1982 on its four-stroke CX500 Turbo. From then onwards fuel injected four-stroke, two-wheeled machines appeared, for a short while, seemingly everywhere. In 2007, Vespa launched the GTS250, its first fuel injected four-stroke, automatic scooter. These days fuel injected, four-stroke automatic scooters are commonplace on the market.
When it comes to carburettors versus fuel injection, the former are easier to set up, adjust and repair. Early mechanised fuel injection systems were notoriously difficult to set up and adjust. As are their contemporary fully digitised, computerised and mapped descendants. Fuel injection gives a better fuel consumption as well as considerably more efficient combustion when compared to guzzling carburettors. Given the technological advances on most four-stroke fuel injected scooters, there’s no need to tinker with a fuel injector as the computerised mapping takes care of everything.