Cycle News is a weekly magazine that covers all aspects of motorcycling including Supercross, Motocross and MotoGP as well as new motorcycles
Issue link: https://magazine.cyclenews.com/i/127760
RIDING IMPRESSION By Kit Palmer (Lett) The 400cc, two-strokepowered Honda EXP-2, which leatures fuel InJection, has an Incredibly broad powerband, very similar to that 01 a big-bore four-stroke. (Far lett) The EXP-2 Is designed to meet emissions beyond the year 2000. ou've probably heard about it, and you might have even seen it compete at this year's Nevada Rally or the Baja 1000. It's the Honda EXP-2, a superenvironmentally-friendly, experimental off-road motorcycle, powered by one' of the most interesting and perplexing single-cylinder, two-stroke motors ever seen in a dirt bike. The EXP-2, which stands for experimental, expedition and expectation of the two-stroke engine, is Honda's way of combining the best of both worlds when it comes to two-stroke and four-stroke technologies. The two-stroke designs have always been known for their advantages in terms of their simplicity, compact size, low weight and highpower output, but are hampered by poor fuel efficiency and drivability, and excessive emission of pollutants. Almost the exact opposite is the case with heavier and more complicated four-stroke engines. But, as issues of energy and the environment arise, the more efficient four-stroke engine has clear-cut advantages over the two-stroke motor, leaving u to assume that four-strokes will most likely power all off-road and street motorcycles in the notso-distant future and that two-stroke engines will become an endangered,. species. Luckily, Honda is not willing to say goodbye to the two-stroke engine, at least not yet, and is determined to design a two-stroke engine that will Jive long into the 21st century. According to Honda, the EXP-2 is "an experimental motorcycle applying AR Combustion- (Activated Radical Combustion), a technology which improves the irregular combustion occurring in the light-load range of conventional twostroke engines." At first glance, the heart of the EXP- 2's single-cylinder, liquid-cooled motor looks like nothing more than a CRSOO engine, but with more wires, boxes and hoses attached to it than a heart patient on an operating table. But in actuality, everything in the motor is unique to the EXP-2. When fuel efficiency and pollutants are of concern, fuel injection immedi~te ly comes to mind, and the EXP-2 features just that - a fuel-injection system. There are two injectors located between the throttle body and the inlet port. According to Honda, using onJy one injector would not be sufficient to supply the full quantity of fuel at full throttle, while keeping the required minimum quantity at idle. The fuel-injection system is similar to that used on Mick Doohan's NSRSOO road race bike. The motor also features an exhaust throttling valve that controls the effec• tive opening area of the port. Both the throttling valve and the fuel-injection system are controlled by two separate computers that are housed in the airbox where the air filter itself would normally be. (Instead, a paper element is mounted