as already said, get it stripped right back to metal and put a couple of plain grey base layers on, then gently sand it back so that its smooth, and then another couple of layers.
plain old spray cans from motor factors and the like will do a decent job. a few keypoints to remember:
do hold the can about 30cm away from the frame ( or whatever the can says )
you make passing movements, so you move towards the frame, bring on the spray, pass over the frame while spraying, let of the spray, all in one smooth movement.
it takes lots of layers to get a good covering … so dont expect it to be fully coloured after the first spray. do your first layer from the correct distance and leave it … NEVER go back over a bit to try and catch a little bit you’ve missed … you’ll end up just putting too much paint down and getting a run. You’ll get it in the next layer.
Once painted, it takes ages to cure if you leave it at normal temp ( days and days ) … so give it that time.