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Motorcycle manufacturers have recognized that highly friction modified passenger car oils can be deleterious to clutch performance, leading to clutch slippage. To address this issue, a JASO specification for four-stroke motorcycle oils was developed in 1999, categorizing oils into high friction oils termed JASO MA and low friction oils termed JASO MB. The high friction oils were preferred for most motorcycles where the engine oil also lubricates the clutch and gears. New motorcycle transmission technologies have increased the number of dry clutch applications which has led to an increased demand for JASO MB oils to improve fuel efficiency. While JASO MB oils contain friction modifiers to improve initial fuel economy, the motorcycle specifications have not addressed the fuel economy durability of motorcycle oils.

A discriminating dynamometer-based test was developed for evaluating cold start and warmup engine performance based on in-cylinder pressure measurements. The dynamometer test offers advantages in time required, flexibility and reduced variability over the vehicle procedure on which it was based. A parametric study on fuel driveability index (DI), ethanol content and intake valve deposit (IVD) rating demonstrated that each of these parameters had a statistically significant impact on engine cold start performance. Simple numerical offsets to fitted models based on oxygen content of the fuel did not account for the difference in engine performance of hydrocarbon-only versus ethanol-containing fuels. The effect of IVD on engine performance did not appear to depend on the DI of the fuel. The benefits of cleaner valves are seen even in fuels of very low DI.