Unscrew the spark plug caps from the wires and look at the copper core in the wires. The seal between the cap and wire is not waterproof and the copper core tends to corrode. If corroded, you can usually snip off a half inch or more of wire to get to clean copper. You may want to check the caps resistance. Factory caps are 9 to 10k ohms. Aftermarket NGK caps are 5k ohms. A weak spark will require a richer mixture I think. By the way, the starters on these bikes are weak. It was about 91 before Yamaha went from a 2 brush starter to a 4 brush starter that cured the slow hot start. The later starters will swap out with yours