I have a Necchi sewing machine The bobbin thread is way loose. What should I do

You can use either 16 or 16J. If your threads are loopy on the bottom side of fabric, the problem is either your needle thread tension is too loose or you have a snag in your needle plate where you have broken a needle. Check needle plate and clear snag if any. Then tighten up your needle thread tension until both needle and bobbin threads are in middle of fabric.

There is loose thread hanging from the lower bobbin, isn't there?

try changing to needle
check the top thread tension--try 3 or 4
clean under the needle plate for lint or loose threads also in bobbin area
make sure bobbin is in correctly

if you have a snap in sewing table remove it first
at the bottom in front of the needle plate area is a bobbin case door
when you open it there is the bobbin case & also should be the feed dogs
always keep the bobbin area clean of lint or loose threads
take note of how the bobbin case is inserted in the bobbin area,, see where the thread tail is at on the bobbin case
then make sure the bobbin is wound correctly or it can cause sewing problems
reinsert the bobbin into the bobbin case the same way it's removed

I also have a necchi sewing machine, the base of your is like the base of mine, if you need a picture of inserting the bobbin,, send me a comment with your email address & I will send you a picture of the threading the bobbin case & inserting it

I also own 2 necchi sewing machines, my mechanical is a 4595,,
lower thread tension
to test the bobbin tension, remove the bobbin case & bobbin & hold it by suspending it byb the thread, **** it once or twice, if the tension is correct, the thread will unwind by about an inch or two.
if the tension is too tight, it does not unwind at all, if the tension is too loose, it will drop too much.
to adjust the tension,, left is loosen & to the right tighten

thread breaks
rethread the machine making sure to get all thread guides
top thread tension usually 3 or 4
replace needle- make sure the needle is inserted correctly
some needles don't work with some thread, here's a tip

Cut 6-8 inch piece of thread of the spool you are going to use for your project
Take the needle you are going to use for the project
& insert the thread thru the eye of the needle
& lift one end of the thread to a 45 degree angle
& if the needle is the right size for the thread it will slide down the thread
But if the needle hangs on the thread you need one size larger needle for the thread

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

if the thread under the fabric is a matted mess
1.the needle thread tension is to loose
2.needle is either to heavy or to fine for the thread
3.check to make sure the thread isn't off the thread take-up lever

Hi - I have a 510 Necchi sewing machine - how do a fill the bobbin?

take out your bobbin and turn it the other way

There is a site that has instructions with how to thread the machine properly. Click here for the www.sewusa.com threading section