I'm replacing the distributor on my 99 nissan frontier and I can't get the ignition timing to 15 BTDC. With the old one I was able to set it to 15 BTDC but on my new one I can't retard it any further than 18 BTDC by turning the distributor. Any idea why this would be? Bad distributor? Something else off that I'm not thinking of? I know I'm not off by a tooth cause I tried that several times.