I currently have an 82 yz490 that runs like a champ. I've read a lot of neg. about the bike, but it's a beast and I love it. I'm also about to get an 84 yz490 that I need to build. My questions are: what is the difference, if any, between the 82 and 84 and I've noticed in articles about different models, i.e. j,k etc...how do I tell what model yz490 I have??