I read back through and thought I saw you have Andy's bracket. My experience with his bracket is that it moved the mounting point back from the carb, and I needed a cable with a longer stroke, so I think you've got the same thing going on.

I run a stock cable and hold down now, but I removed the lip on the back of the cable which allowed me to mount the cable more forward in the hold down. If you're off by 1/4 of an inch or even 1/2 this approach may work for you (vs removing the stop from the pedal).

What is the overall length of your cable? I bet you've got the 24.25 inch one. Mancini sells a 29 inch one with the 3 3/4 stroke, that's the one I bought when I was using Andy's bracket. I just checked and the stroke on it is 3 3/4.