front chainring differential affects derailleur?

David Bruno said:

To force myself to keep the gears low while at the same time not wanting to cross gears, I put a 42
tooth chainring as my big chainring. So my setup is a 39-42....ya it looks pretty silly.

The problem is the front derailleur will not shift up when I put the chain on the 39, nor shift
down when it's on the 42. I didn't change anything with the front derailleur and it worked fine for
a 53-39 setup.

So it looks like the front derailleur just isn't designed for something like this, eh?

You did slide the FDer down when you did this, didnt you?

Quoted message said:

You did slide the FDer down when you did this, didnt you?

would lowering it definately fix the problem? I can see that would help the downshift, but what
about the upshift? It seems like the big chainring catches the chain on the upshift and the 42 just
doesn't catch.....regardless of height.

thanks, David