I have a Singer 29U171A machine and just got it working good with T-69 thread. I wanted to be able to sew with heavier thread, T135/v-138 bonded nylon and a 24/180 needle. The top thread keeps bunching up in the shuttle. I've checked the timing per my manual and it appears correct. Also have tried adjusting the tension of both the bobbin and top thread feed along with the presser foot settings. No joy. Any ideas what I'm doing wrong? Thanks in advance, Tom