Left needle not working on MyLock 634D

Question

I just got a gently used New Home Janome 634d serger and I can't get the left needle to work. The needle was broken but I replaced it with the exact name brand and size, so I cant imagine what else I am doing wrong. It will stitch maybe one or two stitches and then it just carries for a couple of inches and then randomly hits and misses again. Any thoughts?