New exhaust cleaning system to meet domestic emissions standards also improves fuel economy by 25% (Yamaha comparison) To be adopted beginning with 50cc scooter due for release this April

Yamaha Motor Co., Ltd. has succeeded in the development of an "exhaust cleaning system" for 2-stroke 50cc scooter engines to meet the new Japanese motorcycle emissions standards imposed on new models (50cc and under motorcycles) released after October 10 of last year. This system will be adopted on subsequent Yamaha models beginning with the new model "Jog Poshe" scooter scheduled for release in April, 1999.

This new "exhaust cleaning system" is one that includes 1) a carburetor fitted with a "compensator" that regulates air intake to improve combustion efficiency and 2) a "Catalyst Tube" (trademark registration pending) type catalyzer that cleans toxic elements from the exhaust.

Of particular note is the fact that the new "Catalyst Tube" adopts a structure specially developed for 2-stroke engines, featuring a tapered pipe insidethe defuser to house the catalyzer element. Besides the platinum and rhodium of a conventional oxidation type catalyzer, an additional coating of palladium enables the exhaust to be cleaned with a smaller surface area of catalyzer. In this way, outstanding exhaust cleaning performance is achieved, including a large reduction in the HC (hydrocarbons) that has been one of the primary concerns in achieving cleaner 2-stroke exhaust.

The effect achieved by this new "exhaust cleaning system" is a reduction of CO (carbon monoxide) by up to one half and HC (hydrocarbons) by up to two thirds compared to existing Yamaha models. Also, due to the adoption of the "compensator", the carburetor can be given a lean setting to achieve a 25% improvement in fuel economy (Yamaha comparison).

1) Improving fuel economy (25% improvement/Yamaha comparison)
The carburetor adopts a compensator mechanism that adjusts intake air volume in accordance with intake air temperature as detected by a sensor. This makes it possible to adjust to a leaner fuel-air mixture once the engine is running.
Furthermore, the system also features a digital timing advance system that provides optimum ignition timing based on actual engine rpm. The combined effect of these factors produces both cleaner exhaust gas and better fuel economy. In terms of standard fuel economy (30 km/hr), this system achieves a 25% improvement in fuel economy compared to Yamaha's existing scooter of the same class (48 km/liter ? 60 km/liter).

2) Cleaning exhaust gas
After being coated with the usual precious metals platinum (Pt) and rhodium(Rh), the catalyzer surface of the "Catalyst Tube" is given an additional coating of palladium (Pd) in order to better oxidize the HC (hydrocarbons) and CO (carbon monoxide) components of the exhaust gas as it passes through the defuser. The addition of the palladium coating particularly contributes to the catalyzer's ability to clean hydrocarbons out of the exhaust.
As mentioned above, the effect achieved by this new system is a reduction of CO (carbon monoxide) by up to one half and HC (hydrocarbons) by up to two thirds compared to existing Yamaha models.

Note (Regulation year):
Motorcycles of 50cc or under, Motorcycles from 126~250cc: 1998
Motorcycles from 51~125cc, Motorcycles from 251~400cc: 1999