I can not get the thread tension right.

Normally incorrect threading, or incorrect tension. First you have to get the bobbin tension correct, and then move to threading and top tension. If bobbin tension is too tight, you are increasing top tension beyond the capabilities of the thread. It may also be that the spool of thread is faulty. What happens if you use button thread?

Good videos in this link

https://www.google.com/search?q=sewing+machine+thread+tension+problems

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I suspect the bobbin thread has escaped its tension spring. If you give the bobbin thread a quick short tug and the bobbin spool spins then likely the thread is not behind the tension spring. This usually causes hook jam but not always.



First be sure you have threaded per machine instructions... see below.



Next turn handwheel and position needle at the high point of stroke (always when loading bobbin). Remove and re-insert bobbin. Now, to be sure the bobbin thread is fully positioned behind the tension spring, before you move the bobbin thread into the notch, place your right index finger on top of the bobbin spool to prevent the bobbin spool from turning. Hold thread snugly (in slight tension) as you move it towards the back of the notch. You should feel the thread slide in place behind the spring. Let loose the spool and lightly pull thread. Note the resulting change in tension. (don't forget to set top thread tension back to a more normal setting)



Comment here if you require further assistance.



If you need... your manual may be downloaded at no charge from the Janome site.
https://www.janome.com/siteassets/support/manuals/embroidery-models/inst-book-mc350e.pdf

Not sure what the root of the problem is but I can help you through some fundamentals.

With bobbin thread unspooling from wrong direction the bobbin thread will eventually escape from the bobbin tension spring and will loop on top side of fabric. The bobbin thread must unwind CCW.

Not sure why bobbin tension seems high when loaded the correct way. Suggest a couple tests, top thread first.

To test top thread feed and tension, place presser foot up and needle up. Select a tension setting of approximately four (4). Make a long slow steady pull of top thread. The thread should advance easily through the needle eye with out hesitation or snagging. This is "no tension" of top thread as foot is up. Any snagging would imply uneven feed from top spool or miss-threading.


Now place foot down and make another long slow steady pull of top thread. Note the difference in no tension (foot up) and selected tension (foot down). Again the thread should advance through the eye of the needle without snagging or abrupt change in tension.


Now with the bobbin loaded, bottom thread brought to top, needle up, make a long steady pull of the bottom thread. It should advance smoothly without snagging or abrupt change in tension. It should have a similar tension to top thread foot down in previous top thread test.

When loading the bobbing, as you draw the thread into the notch with left hand, and prevent the bobbing from moving with right hand, you should feel the thread slip into place behind the tension spring. It should still move easily, just under tension similar to top thread foot down.

I believe this model has a transparent bobbin cover. After bottom thread is brought to top, when ever the needle is up, the bobbin thread should be visible crossing over the top of the bobbin spool so long as there's sufficient tension on top thread.

Comment below with your findings and I'll assist further if need be.

You have not got is threaded on top right. Do this test, rethread your machine with the presser foot up, pull thread, it should move smoothly, now put the presser foot down, pull thread, it should barely move. This seats the thread in the tension discs. See if that works.

Try this little trick, rethread it and then with the presser foot up pull on the top thread, it should move smoothly, now put the presser foot down, the thread should barely move. This sometimes seats the thread in the tension discs the right way. I have my tension set at 3 but each machine is different.

Your top threading is not right. Rethread, check your tension on your thread by pulling on the thread with the presser foot up, it should be smooth. Now, lower the presser foot and try to pull it, it should barely move. If, either is not happening, you are not threaded right, it depends on having the right tension.

"Birdnesting" occurs when there is no tension on the needle thread to pull the bobbin thread. This is easily corrected by rethreading the machine, following the threading path carefully and making sure the thread is fully engaged in the tension mechanism.

oil the shaft for the presser bar and keep moving it up and down(it may take a while) until it moves freely. Always use Sewing machine oil Not 3N1 oil.
Tension:
If the thread is loose on the bottom of the fabric, it's actually the top thread is too loose. Think of 2 little elves playing tug of war in your machine, one on top and one underneath. If you have loops on bottom, the top needs to pull harder (tighten top tension). If you have loose thread on top your top tension is probably too tight and your bobbin thread too loose

Setting bobbin case tension:
Put wound bobbin in bobbin case. Thread it in case. Hold the thread and carefully let go of the case only holding bobbin thread. The case should NOT move. Quickly let your hand drop 2-3 inches to let the bobbin case free fall for 2-3 inches, the bobbin case should move slightly then stop. It moves because it let’s a little thread off the bobbin. It should then stop .5"- 2" of thread should release. If so, your bobbin case tension is right. If it’s right then begin to look at your top thread tension. Always Always start with a properly adjusted bobbin case, then adjust your top tension accordingly.

The bobbin tension sounds too loose. This will help if you have a bobbin case and not a drop in bobbin. Let me know if you have a drop in bobbin:
Setting bobbin case tension:
Put wound bobbin in bobbin case. Thread it in case. Hold the thread and carefully let go of the case only holding bobbin thread. The case should NOT move. Quickly let your hand drop 2-3 inches to let the bobbin case free fall for 2-3 inches, the bobbin case should move slightly then stop. It moves because it let’s a little thread off the bobbin. It should then stop .5"- 2" of thread should release. If so, your bobbin case tension is right. If it’s right then begin to look at your top thread tension. Always Always start with a properly adjusted bobbin case, then adjust your top tension accordingly.