I have a Necchi 4900 and the thread catches on the bobbin holder , moves the bobbin holder out of place , james , have taken it out cleaned everthing under the bobbin and takewn the underneath cover

Here's the manual:

Janome MEMORY CRAFT 4900 QC Instruction Book Inserting The Bobbin

Install a brand-new needle. If it continues to miss the bobbin thread, take it for service. It most probably has a needle/hook timing issue.

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Your hook is moving correctly. Not all machines do a continuous circle. If it's not catching the thread, the timing is off. It's a great machine, and worth every penny to have it serviced.

did you find the tip of the needle? Also you may have a nick in the metal where the needle hit and broke.It can catch on other parts and need to be sanded or replaced.One time I had this issue and I found the tiny broken tip under my bobbin case.

it is very possible that the machine could have jumped time
& needs to be checked at a sewing machine shop, because a
sewing machine technican has the tools to retime the machine
if it is out of time

Do you have a manual for this machine? You need to follow the cleaning instructions and remove the needle plate, and clean under the bobbin holder. I've attached an image from my Janoma 6500 manual, I think yours has a top loading bobbin inside a magnetic bobbin case so this info should work for your model. There may be a little triangular shaped tool in your kit but any short flat blade screwdriver will remove the two setscrews. (always good idea to unscrew off the pressure foot and take out the needle first so you've got room to work).

PLEASE NOTE: If you've never pulled this bobbin area apart before, good idea to snap pics with your digital camera as you go to refer to and for reference next time!!

This uncovers the bobbin holder area, you'll see there is a black plastic holder which your bobbin goes into which has the tension device on the side and this then sits inside an outer metal casing which is the hook race. The bobbin holder is held there by a magnet underneath it and sits up against another little stopper. Look at the bobbin case and the stopper, there should be two red marks that must line up. Are they???

If the answer is no, then you need to remove the bobbin case, clean out any lint and fluff using your little brush that came with the machine, and you may also have pieces of thread caught in here too. Once clean, place the bobbin case back into the outer surround, under the other piece and lining up the two red marks. This is where photos are so helpful.

Now replace the needle plate and screws, pressure foot, pop in a new needle and thread everything up again.

If the thread continues to catch then you may have managed to damage the bobbin case; as they are plastic if they move out of position the needle can catch and burr or pierce them. If this has happened you could try to smooth out the burring with an emery board or similar. Or you may need to replace it if damaged badly. I've changed mine twice so far because I've pierced it with the needle several times.
I hope that this helps you out, good luck with your machine.

Have you got the thread aerial up and using the thread cap on top of the spool of thread to ensure it feeds off smoothly. Also need to look at the thread spool, some of them have a little cut in the top where the thread end is placed to keep neat. If the thread is catching on this, just turn the spool up the other way and use the cap to hold thread away from the edge of the spool.

Gutterman is a good quality thread so you need to check that there isn't something in the thread path catching the thread and affecting the tension which is why it usually breaks. It could be a burr on the bobbin holder, the black plastic tensioning device which sits on a magnet. I have managed to damage 3 of these with my 6600P by trying to stitch too heavy weight seams, the bobbin holder moves and then the needle strikes it, once to the point of piercing right through it!

So have a look in the bobbin area, refer to your manual if you haven't removed the bobbin holder before. There is two little red marks that need to line up when it is in the right location. If you can see damage on the bobbin holder, you could take it out and try to file down the burring with a nail file or very fine grade sandpaper and then put back in again. The needle thread could be catching on a burr as it comes around during the stitch process.

Also, look at the top tension dial, turn it to zero and clean between the discs with the selvage edge of a clean piece of cotton waste. Then turn tension back to 5 and thread up everything and try again.

If you have tried all the above without success then perhaps take it back to the dealer and ask them to test sew it for you and see if they can spot the problem.

Check the bobbin tension and that the thread is tight around the bobbin. Make sure that the bobbin is in the right way around - the bobbin thread should double back on itself coming out of the bobbin holder.

Make sure the bobbin has a 3-5 inch thread tail
Then make sure the top thread has a 3-5 inch tail
Then hold the top thread tail with your fingers (away from the needle)
& use the hand wheel on the right hand side of the machine to slowly
Lower the needle in the bobbin area & see if the bobbin thread will pick
Up that way

ever tried adjusting the thread tension control? clean if possible
tighen it more, loose tension adjustment causes loose stitch and tangling of the thread.