Double check how you are supposed to thread it when doing the bobbin. On mine I used to thread them thru the needle because when I did them thru the bobbin guide it didn't what yours is doing. I would get so frustrated. Then I took a class about a yr after I had my machine and the best thing that I learned in the class that I wasn't putting it thru the one guide that you use to thread your machine first and then around the bobbin guide. Now they all wind great rather thru the needle or when I'm sewing or just winding bobbings, no more lopsided bobbins. I also slow down the winding too.