Hello, I'm fairly new with sewing. I have a Kenmore 15718. I'm sewing a leotard with a light weight stretch material. I'm using the blue needle (I believe it's 75/11) and have no troubles with the material itself. However, when I try to add the elastic, the needle thread sews alright, but the bobbin thread starts to get all jumbled up in a big mess. Everytime it does this the machine makes loud noise and as I turn over the material I've got a mess of thread on the bottom. I've tried using both the blue needle and a ball point 90/14. I've also messed with the needle tension betwen 2 - 4. For this machine it has a setting on it specifically for sewing elastic which I have been using. Nothing seems to help. What am I missing and how can I get the elastic to sew on good?

Thanks