When we thread the serger . the thread is still skipping

Are you using the corfect serger system needles in it? Most domestic sergers will take the regular domestic needle 130/705X but work best with a serger needle with has a groove down the front as well as the regular back scarf. This helps with the thread pickup from the looper by the needles. Sergers also run much faster than domestic sewing machines so the tolerances are very fine.

My Bernina came with ELX705 needles and it does run better with these in it. Also you need to use mid size needles, don't go too small, probably a size 80 or 90 is best.

Check out this page for some good info as the different serger manufacturers do have their own recommended needle sometimes. http://sewingmachine221sale.bizland.com/store/page78.html

Always refer to your manual (or ring the manufacturer if lost) to double check what needle they recommend be used in your serger, it does make a difference.

First thing to try is installing brand-new sharp needles in your serger. Second thing is to re-thread all the threads in the proper order specified in your owner's manual. If you don't thread correctly, your serger will probably never serge properly.