Try out Krylon "farm and impliment" paint. I used it on a frame and it worked very well, seems to almost be an oil-based paint but I'm not sure. It fills in slight imperfections and dries tough and shiny. The only issue you may have is the color selections are limited. john deere green, caterpillar yellow, farmer red, ford blue etc. Real basic selection but really durable and designed to use on metal. Sprayed mine over a smoothed out beat up original paint with some parts sanded down to the metal and it looks great.
pics here: http://motorbicycling.com/f26/motori...tml#post189445