sax2 and wheel mouse

Try as I might I cannot get my new wheel mouse to scroll. I set it up with sax2 to emulate 3 buttons and set the z-axis positive=4 and negative =5. There were radio buttons for z-axis in sax2: X, Y, Button, No. Setting to Button caused the right button menu to pop up with a wheel turn; Setting to Y causes the cursor to move by the increments set in positive/negative. I started imwheel in .xinit. What am I doing wrong?