I have mc9900 janome when trying to embroidery on t-shirt material threads bunch up in back and I end up with holes in shirt

Where is the thread bunching up?Make sure you have the correct thread for the needle size and material. Make sure that the thread is not old and that the needle is not bent. also, check the top tension in relation to the material being used. You could clean out the feed dogs in case there is lint jammed in there too. :)

increase the needle thread tension

Adjust the bottom tension, it needs to be looser. The top tension may also be too tight. Try loosening them just 1/4 turn and see if that helps.

Sounds like bird nesting.
The #1 thing is to install a brand new needle (old, worn, nicked, or bent needles can create a lot of havoc).

Remove all the thread from the machine. RAISE the presser foot and rethread from the beginning verifying that it is threaded correctly. Make sure the bobbin is loaded and threaded in the bobbin case properly.

WHY IS THREAD BUNCHING UNDERNEATH MY FABRIC

Why Do Get Bunched Up Thread Under My Fabric

8 Tips to Fix Birdnesting in Embroidery
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My machine is a bit different than yours but there is a way to back up your Janome 10 stitches at a time. Here is a thread that I initiated at the janome embroidery forum that should help you. Digimad included a detailed help for me. It should direct you to get you going again. Do join the forum the gals there are generally a great bunch and very helpful.

http://content.janome.com/fusetalk/forum/messageview.cfm?catid=7&threadid=4317

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

A good place to see what machines are selling for is Ebay. That's where I sold a sewing machine and an embroidery machine.

It helps to know your product and machine embroidery lingo.

What are cassettes? Floppy disks? These make the machine borderline obsolete.

Memory cards are still around, but most EM now have USB connectivity or USB flash drives.

Satin thread? Embroidery machines use Rayon or Polyester embroidery thread.

Having had the machine recently serviced is also a plus.

the feed dogs are what pushes on the material from underneath. perhaps they have been lowered ? You do that for free hand or embroidery work,
look for a lever at the back, behind the bobbin area. That's where they are in the janome, which is related to the kenmore somehow; good luck

the needle thread tension is wrong
bunching up under the material indicates that it is too loose

after 8 years of sitting, the machine needs to go to the shop so that areas that are inaccessabe to the sewer can be cleaned and serviced by the tech. also check the upper threading of the machine. the tension is changed if threaded incorrectly. bunching under the material is caused by several different reasons. I would first have the machine cleaned and serviced by the tech, and let them know it has been 8 years since use. we all begin walking by taking one step at a time.
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