Machine is skipping stitches

If the zig zag function on your Elna Carina sewing machine is not working, there could be a few possible causes:

1. Incorrect stitch selector: Make sure you have selected the correct stitch on your machine. Double check that you have selected the zig zag stitch, and not accidentally switched to another stitch.
2. Incorrect stitch width: The stitch width knob on your machine controls the width of the zig zag stitch. Make sure that the stitch width is not set to zero, as this would prevent the zig zag function from working. Adjust the stitch width to the desired size.
3. Tension issues: If the thread tension is too tight or too loose, it can affect the zig zag stitch. Check your thread tension to make sure it is set correctly.
4. Clogged machine: Dust, lint, and debris can accumulate inside your sewing machine and affect its performance. Clean your machine thoroughly, including the bobbin area and the feed dogs.

If none of these solutions work, it may be necessary to have your machine serviced by a professional.

Sounds like the needle alignment is out.
This website has some instructions on how to properly set it up and also has manuals too.
http://welcome.solutions.brother.com/bsc/public/us/ca/en/faq/faq_list.html?reg=us&c=ca&lang=en&prod=hf_cs8072eus&Cat=53

It sounds like maybe the bobbin tension is too tight. It is pulling the top thread down to the bottom of the fabric. If you tighten the top tension it causes the fabric to pucker. If you loosen the top tension, more of the top thread will show on the bottom. Correct tension is when the top and bobbin threads meet in the middle of the fabric.

Understanding Thread Tension on Your Sewing Machine

Is your bobbin threaded correctly? You should be able to pull out the thread slowly while feeling it very slightly holding back. It should not pull out easily or quickly.
Could be something wrong with your tensions, try adjusting the upper tension first by starting at the middle setting and working gradually higher and then lower till you get a neat even stitch.

According to the manual, you should not need to adjust the bobbin tension (and I located other sites which stated the bobbin tension cannot be adjusted on this machine). Apparently, all the tension adjustment is accomplished through the upper thread::
"EN Thread Tension Upper thread tension Basic thread tension setting: "4". (1) To increase the tension, turn the dial to the next number up. To reduce the tension, turn the dial to the next number down. A. Normal thread tension for straight stitch sewing. B. Thread tension too loose for straight stitch sewing. Turn dial to higher number. C. Thread tension too tight for straight stitch sewing. Turn dial to lower number. D. Normal thread tension for zig zag and decorative sewing. Correct thread tension is when a small amount of the upper thread appears on the bottom side of fabric. Lower thread tension The bobbin tension has been set correctly at the factory, so you do not need to adjust it. Please note: - Proper tension setting is important for strong seams. - There is no single tension setting appropriate for all stitch functions, thread or fabric. - A balanced tension (identical stitches both top and bottom) is usually only desirable for straight stitch construction sewing. - 90% of all sewing will be between "3" and "5". - For zig zag and decorative sewing stitch functions, thread tension should generally be less than for straight stitch sewing. - For all decorative sewing you will always obtain a nicer stitch and less fabric puckering when the upper thread appears on the bottom side of your fabric. 1 A B C 22 D"

Doing further research, I found this statement on a machine review site:
"After reading reviews online from where I've bought my drop-in bobbin machines, I think many of the negative reviews are due to the bobbin thread coming up without laying across the bobbin. It can cause the stitches to look very sloppy and no amount of tension adjusting can fix the stitches."

There are several machine review sites wherein 4423 owners stated their disappointment in the 4423's performance. Some said the machine failed almost immediately and others said the machines developed problems when sewing heavy fabric.

Adjust the tension

sounds like the timing is off and will need a service call to get it reset. your local fabric store should know who you can call.

it's very possible that the machine is slightly out of time & needs to be service at a sewing machine shop
is the fabric & thread & needle compatable with each other?
did you use every thread guide when threading the machine?
is the bobbin in correctly?
is the bobbin warped?

The three front dials are as follows....left to right-Stitch width, type of stitch, and stitch length. The dial on the top adjust the top tension.

For straight stitch you want 0 stitch width, straight stitch, 3 for stitch length.

For zig zag you want turn your stitch width to how wide you want the zig zag, choose zig zag stitch, and choose how close you want the stitches to be on the stitch length dial. Practice on a piece of fabric. Usually for zig zag you will want to loosen your top tension a little bit.

Because it is almost a straight stitch but the needle continues to move in a zig zag fashion is reason to believe it is in a long stitch. By changing the number of stitches per inch there will be a very noticeable looking zig zag stitch.