In the page that you posted you will want to comment out line 323 so that it looks like this:
/*marker_1_<?php echo $sitelat_id; ?>.openInfoWindowHtml(address_1_<?php echo $sitelat_id; ?>.infowindowtext);*/
You will also want to comment out line 353 so that it looks like this:
/*marker_1_<?php echo $sitelat_id; ?>.openInfoWindowHtml(address_1_<?php echo $sitelat_id; ?>.infowindowtext);*/
The final entry that I found was on line 378, you should also comment it out so it looks like this:
/*marker_1_<?php echo $sitelat_id; ?>.openInfoWindowHtml(address_1_<?php echo $sitelat_id; ?>.infowindowtext);*/
It looks like you have correctly altered the zoom level from what I can see in the code. When I viewed the page I could see many entries, greater than 25 just from a quick count. Have you tested all of the locations independently to confirm that each of them can be mapped? You might be having a problem with a location that cannot be mapped throwing off the rest of the results.