I have a road bike with Shimano 105 and I'm having issue with the FD/Left Shifter. I can't get the adjustment just right. The shifter is a triple and the crankset is a truvativ rouleur double.

The problem is that I can't seem to shift to the large chainring unless I am at lease halfway through the cassette. Also if I shift down to the smaller chainring and I'm not in the lower half of the cassette the chain sort of falls between the chainrings and doesn't engage the smaller ring.

The limit screws don't seem to do anything when I turn them either.