In 1969, the FIM—citing high development costs for non-works teams due to rules which allowed a multiplicity of cylinders (meaning smaller pistons, producing higher revs) and a multiplicity of gears (giving narrower power bands, affording higher states of tune)—brought in new rules restricting all classes to six gears and most to two cylinders (four cylinders in the case of the 350 cc and 500 cc classes). This led to a mass walk-out of the sport by the previously highly successful Honda, Suzuki and Yamaha manufacturer teams, skewing the results tables for the next several years, with MV Agusta effectively the only works team left in the sport until Yamaha (1973) and Suzuki (1974) returned with new two-stroke designs. By this time, two-strokes completely eclipsed the four-strokes in all classes. In 1979, Honda, on its return to GP racing, made an attempt to return the four-stroke to the top class with the NR500, but this project failed, and, in 1983, even Honda was winning with a two-stroke 500.