Ok, so I have a 1990 xv535, that I bought used a week ago. Here is the issue, it seems to run rich, and I am only getting about 100mi out of a tank of gas. I ran seafoam through it, and changed the spark plugs, and it accelerates smoother now. One thing I did noticed when I changed the plugs is there was oil on the threads, and the end of the plugs was charred black. I know that the black on the plugs is from the bike running rich, but not sure why there would be oil on the thread of the plugs. I need help with both issues. I am worried that there is a major problem, and that's why there is oil on the plugs. Thanks for the help!