How to thread Necchi 4575

Perhaps this will help:

Necchi 4575 manual

Instruction Manual Necchi 4575

How to Thread Necchi Sewing Machine

try a different bobbin
make sure the bobbin in turned the right way in the bobbin case
also the machine may have a timing problem, and having it checked to would be a good idea.

here's a link for inserting a bobbin into a machine
http://www.youtube.com/watch?v=ZX3LjiYOLsg

here's some links for a manual for the machine
http://www.sewingpartsonline.com/instruction-manual-necchi-4575.aspx

http://www.sewingpartsonline.com/instruction-manual-necchi-4575-download.aspx

There could be a simple solution or one that needs professional assistance, try inserting a new needle with making sure that the flat side is facing away from you. Also, try a light sanding in the hole that the thread comes through. Try rethreading with different thread and making sure that you leave enough of a tail on the bobbin thread. If, this does not work you may need to have the timing checked. good luck

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.

you might try checking your needle to see if it's bent-roll on flat surface to see if it roll correctly
or blunt or damaged
some sewing machines bunch up like that when the thread come off the thread take up lever
also check the top tension
check for lint or loose thread in the bobbin area
check to make sure the bobbin is wound correctly

There is a screw on the bobbin case to adjust if you have too, the thread should pull through with slight resistence, if it is too loose tighten the screw a quarter of a turn at a time clockwise and test and keep adjusting if you have to.

Top tension about 4 or 5 makse sure you have the bobbin in the correct way round and make sure you can just pull the thread through with slight resistence.

Timing is off, is is possible that you broke a needle or sewed over a pin. timing needs to be re set by a professional.

I've found that my machine doesn't like Coats & Clark thread; I have to feed it Guterman