There are a number of reasons for the problem you describe, IMPE: it may be tension settings, but it may also be as simple as having the needle in backwards, or the wrong size/type of needle & or thread. The bobbin may be wound improperly, or the bobbin &/or case may not be inserted properly - & sometimes, the type of fabric can cause this as well.

Have you oiled the machine recently? It may need it.

Hopefully, it's not timing - that takes a pro to fix.

Start by unthreading and rethreading top and botton according to the directions in the manual (you do have a manual, right?).

Too much thread on the underside of the fabric is almost always top thread - the result of insufficient, or no top tension. Make sure the presser foot is UP when you thread so the thread is firmly seated in the tension discs. Also, do not attempt to remove your work from under the presser foot unless the take-up is in its highest position.

If you don't have a manual, you can probably find a pdf copy on www.ismacs.net. Follow the instructions for threading the top and make sure the bobbin is threaded properly.

Also, make sure you have a good needle and that it's been put in correctly. Many times, it's easy to put the needle in wrong or thread it wrong. So check that too.

If it is the tension, I'm no expert on that, so hopefully someone else can help with that aspect.

Elaine