Other than the change from the white motor to the silver one in 1998 the 951 remained the same throughout production,stock hp was 130,in 98 they changed the airbox design to one with snorkel intakes that took in air at the top of the cylinder head,the path that air has to travel to reach the cylinder is quite long,snorkel intakes would be an easy mod and you could put the intakes wherever you wanted them. These engines are not ticking time bombs as a matter of fact I have only seen one destroyed,a new set of cases,a rebuilt crankshaft and pistons and rings and it was back together and still runs 60 mph = to this very day,that was built close to 10 years ago.I couldn't count the number of Yamaha 1100-1200 engines I have seen totally destroyed on both hands and both feet combined.