Is your 600 XLT a triple ? I recall a guy that also had a Polaris 600 triple and he eventually jetted each cylinder differently. His sled was slightly modified for the mountains (pipes, K &N and light wieght trailing arms ) and he played with the jets to get all clyinders the correct plug color and piston wash. I don't understand it ( why each cylinder was different ) but I know he played arround with the jetting. I think the PTO cylinder was the richest jet ( which is ass backwards from your prolbem ) .
Sorry for the grief - Good luck Ponyboy
