I just had some cable guides brazed on and now I'm looking at painting the frame. Does the paint need to be completely stripped or can i just sand and roughen the old paint up before i paint it?

Sand the undamaged areas, sand and primer the bare metal and use a decent type of paint- acrylic enamel, not krylon cheapstuff.

Thanks for your response. Do i have to sand until i get to bare metal? If so, can i just use some sort of naval jelly to strip the paint then sand?

The main thing is a clean surface, whether on top of some old paint or bare metal. However, the "level" difference between bare areas, primed areas, and painted areas, no matter how old, will show up when you repaint.

you can remove all of the old paint, if you aren't into saving the old finish, using a variety of strippers. The safest is something like Citrus-strip, the fastest that I've used is Aircraft Stripper...but I've already had (fingers crossed) all of my children.

ok great..thanks for your responses. Looks like i'm stripping all the paint off then sanding..

It seems like sanding the original paint down to the primer wouldn't be a bad idea. When I stripped a frame, my chemical strip when right through the color but barely did anything to the primer. I feel like almost no rattlecan or other home paint job can adhere that stubbornly to the bare metal, no?

If you do have primer left after the chemical strip, no problem, just make sure that:
1. There is no trace, as in zero, of the stripper left.
2. Give the primer some new 'teeth' by sanding it lightly with some fine grade paper. You can even get 2000 grit at WallyWorld now. (Can wet sand if you like, but dry thoroughly)
3. Use a tack cloth on the newly sanded primer.
4. Paint away.