My new sewing machine, just opened to use, is bunching thread on the underneath or bobbin side when I attempt to straight stitch. What is causing this to happen. Thanks.

hi Lois.
this is all i could find out.
Check Your Tension Settings. Looping underneath the fabric usually occurs when there is not enough tension in the needle thread to pull the bobbin thread. Sometimes thread bunching can be caused by something as simple as the tension dial being inadvertently turn.
or try this link.
WHY IS THREAD BUNCHING UNDERNEATH MY FABRIC
or this one,
Sewing Machine Thread Bunching Up Here Why .
if you go to this link a little window might open up in the middle of the page just close the little window down.
or this.

The bobbin thread is bunching up Google Search

adjust the tension to a appropriate setting,
See the video here.
Sewing Help Sewing Machine Problem Thread Bunching Under Fabric
The knob and its location can differ based on the model of your sewing machine.

Skipping stitches and thread breaks
Skipping stitches and thread breaks

Sewing Machine Thread Bunching Up? Here's Why!
Sewing Machine Thread Bunching Up Here Why

you need to tighten the tension control knob

try changing the needle--use a needle according to the fabric
being sewed
if thin fabric is being sewed try using a stablizer
rethread the machine top and bobbin--use every thread guide
make sure the bobbin is inserted correctly and turned correctly
in the bobbin case
also try adjusting the top thread tension just a little

Try these suggestions
1. Change needle
2. Rethread the machine--top --make sure to use every thread guide
3. Take the bobbin out --make sure it is inserted correctly into the bobbin
Case, & make sure the bobbin is turned the correct way
4. make sure the thread has not come off the thread take up lever
5. Clean under the needle plate & in the bobbin area for lint or threads

try rethreading the machine top & bobbin
check to see if the thread has come off the thread take up lever
try changing the needle
also make sure the needle & thread & fabric are compatable

try putting in a new needle---flat side to the back of machine
try rethreading the machine
make sure the top thread is on the thread take up lever
clean under the needle plate & in the bobbin area for loose threads & lint

Try these time savers:
Test your thread quality to start, thread your machine and LIFT the presser foot (this opens the tension disks). Pull your top thread straight back. If you feel no tension no mater how much thread you pull, your thread is good. If that your machine passes that test, then let me know, we can go to step 2. If not, try different spool of thread, same test until you get a smooth pull (tip: always check your thread this way when you thread your machine)
Step 2:
Pull on your threaded bobbin thread while it’s in the machine. Does it pull smooth and even? If so, go to step 3. If not, try a new bobbin (bobbins get bent or distorted if wound too tight).
Clean thoroughly in the hook and bobbin case area and oil 1-2 drop is all.

This is a very common problem with really lightweight fabric and can often be cured (if doing straight stitching) by using a straight stitch needle plate and foot. The wider needle plate and foot openings on newer machines give the machine/thread a wider area to pull the fabric into the machine. By using a straight stitch plate/foot you remove the wide opening, eliminating the majority of the problem.

Also - try using a specially coated needle (Teflon or other non-stick finish). The thread feeds more smoothly through the needle and the needle more smoothly through the fabric, causing less drag into the needle plate opening.

Hope this helps. Don't hesitate to respond to this if you have further specific questions. We're always happy to help

Happy stitching,
Kim & Linnette
www.sewingexpressions.com