As the years have gone by since its introduction in 1985, so has its rated HP. The reason for this is due to more restrictive exhaust and noise emissions, mandated by the EPA. Every several years the manufacturers must comply with lower emission standards and some models must be detuned further in order to comply. Understand that when Yamaha releases their rated HP for any given motorcycle they offer they are telling you the measured power at the crankshaft, not the rear wheel. In 1985 it was rated at 145. It remained at that spec until at least 1988 or later. At some point it was reduced to 140 and later reduced to 133 where I believe it remained until it was superceded by the completely redesigned 2009, rated at 200. In all probability your 1998 is in the 140 catagory. I think it was after 2000 that it was reduced to 133. From my recolection, there is no power difference between the Canadian and US spec models. When comparing directly, the difference in acceleration between the 08 and new 09 is utterly staggering!