I have a used (recumbent) bike with a Ultegra front derailleur (3 gears). I can't for the life of me seem to get it lined up properly. I've read you are supposed to have about a 2mm gap between the bottom of the cage and the top of the gear at the top; however if I do this then the back of the cage is rubbing the gear. (it's possible my large gear is too large?)
Likewise there are several bumps inside the cage to aide in shifting. Is there a diagram somewhere of where the chain should pass through in the small/medium/large gearing? Right now my middle gear passes through the tighest part of the cage (where it is dented in on both sides)
Not exactly. If you've got a 10sp FD (#6603), the back plate of the cage is really designed for a 13-tooth minimum difference between the middle and large rings; the Ultegra "10sp" cranksets have 52/39/30 rings. If you're using a chainrings with a smaller difference (e.g., 50/39/30 or 52/42/XX), then the back plate will contact the middle ring before the derailleur can complete the shift to the large ring when the FD is positioned at the recommended maximum height.
I'm using an Ultegra 6603 FD with 50/39/30 rings. I had to mount the FD a bit higher to clear the middle ring. As it turns out, shifting is excellent, it's not needed a single adjustment in thousands of miles, and I've never thrown the chain past the big ring. I suspect a 10t difference would have exceeded the specs enough to cause noticeable initial setup issues and occasional thrown chains.