In my experience, the fuel line pinch method on the Magnums is not a good method until you're close. The easy way to set it is to set the high end a little rich of peak, then bring your throttle down to the lowest speed it will continue to idle at (this may be fairly high to begin with). Now use a long thin screwdriver to slowly adjust the low speed needle until the engine begins to run smooth. Go back and reset your high needle (yes it will change). Bring it down again to the lowest reliable idle (it will be lower). Repeat this cycle until you have a nice reliable low idle (should end up arount 1750 rpm or so, depending on prop), and smooth transition from low to high with no hesitation. Additionally, you'll find that when you come down to idle from high speed, the engine RPM should be pretty stable (not speeding up or slowing down as it sits). You can then check it with the pinch test, but I'm willing to bet you'll be right where you want to be.

Brad