to start my car is a 80 white ls with an 85 12a with rb stock port holley setup, rb header and muffler. the car runs pretty good, as I just drove it on a trip about 250 miles round trip. but I noticed when I got back the right back of the car above the muffler was yellow. i have the omp hooked up like rb says but is it possible its getting too much oil to the carb?

 

My bet is that you are seing your rich exhaust on the paint. I've seen varying degrees of this on my lexus and some hondas around town.