Is the Isacord thread you are using embroidery thread? It should say a wt. such as 30 or 40.
Are you using the same thread on the top and the bobbin?
In my Juki I have the best results if I use a Topstitch needle and a 90/14. Usually get Schmetz.
It seems like your needle could be pushing the fabric into the needle plate rather than pushing thru. Do you get a nest of thread on the bottom?