Knotting up underneath on model 121r New Home Sewing Machine

Search the internet for:

Manufacturer + Model + the word "Manual"

plug it into your charger cable and 110volts, there is only one connector that the charger cable will go into.

Could be what is called thread nesting or bird nesting.

The first thing to try is installing a brand new needle in your machine. Then try the following suggestions:

sewing machine birdnesting

WHY IS THREAD BUNCHING UNDERNEATH MY FABRIC

3 Common Sewing Machine Problems and How to Fix Them

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you may not have the tension adjusted correctly

Ah ha! ok. Good machine. Take a piece of string and make your measurement with it. Or take of the existing belt and measure that.

Most belts can be had these days with an exception of some of the direct drive friction tires.

I got my last singer belt directly from it worked great!
http://shop.sew-classic.com/

a heavier drapery fabric is going to require a needle & thread for that specfic fabric

Check YouTube for some great video advice. I was checking for tension issues and she addressed "bunching" issues too. Recommended teflon bobbin washers!

Manuals are available on the Riccar site.
http://www.riccar.com/help/manuals/
Have a look at a few to see if any are similar to your machine. There are quite a few but I'm afraid but that's the only way I can think of doing it without seeing a picture of the machine.
Most machine have the model number written on them somewhere, but that doesn't sound like the case here.
Hopefully your manual will be able to tell you which settings are correct for your machine in able for it to sew properly.
Hope this helps!

1.check the needle & see if it's bent--if so replace
2.lay the needle on a flat surface & roll the needle over if it doesn't roll true replace
3.check for blunt needle-if needle makes a popping sound when needle penetrates fabric
4.needle is not all way up in holder
on my mechanical sewing machine sometimes the threads come off the take up lever, that causes the thread to bunch up under something I'm working on
also check thread in bobbin

First check that there is no thread remands in the hook race.Try tightening your bobbin case cover little by little.