conversion-single master cylinder to dual

Make sure the calipers are positioned correctly and not upside down. Is the bleeder screw on the top or bottom of the caliper? The bleeder should be at the top.
Make sure the M/C and proportioning valve has been bled. Normally you will have to wait a day and let everything settle and bleed again. Another way that I have done before is fill the M/C, crack the 4 bleeder valve,s and let gravity do the job. You do have to keep an eye on the fluid level periodically.