Stitch tension problem - bobbin thread lies flat or bunches. If you increase the needle thread tension there is no improvement - even at the highest needle thread tension the bobbin thread is a mess. Any suggestions - I have checked the bobbin thread tension also - turned the screw on the case and shook the thread and case to see if it dropped evenly. This is a Consew 7360R Industrial machine working on patio - outdoor fabrics. I have tried size 18 and 16 needles and 3 different size threads - all stitch the same.

what you describe indicates that the needle thread tension is too loose
it is not pulling the bobbin thread up and that is creating the birds nest under the material

Before you begin sewing, it is always helpful to pull up the bobbin thread up through the project fabric.

How and Why to Bring up the Bobbin Thread

Before you take the first stitch, be sure the thread take-up lever is at its highest point. Then, gently hold the two thread tails in your left hand and slowly begin to stitch.

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First, try a brand new needle.

Second, consider using a better quality thread. By all means, AVOID old or bargain bin threads. Coats & Clark used to be a standard, but thread quality has improved over the past few years, so you may want to check out other brands like Aurafil, Superior, Isacord, etc. Also, cotton wrapped polyester thread releases thread lint that contributes to build-up of gunk in the machine. Some sewists have noted that they experience more sewing issues when using C&C threads. However, some machines will do better with certain thread brands than others, so some experimentation may be beneficial.

Third, check the stitch on your sample again. Generally, when thread loops appear on the underside of the fabric, it is the upper thread that is the problem. If loopy threads appear on the top of the fabric, it is the bobbin thread that is the issue. You can even use a different color in the top to help distinguish which thread is the problem.

Fourth, when threading the upper thread, Always Raise the Presser Foot during the threading process so the tension disk is released and the thread can seat properly. "Bird nesting" occurs when the thread is not seated in the tension disk.
Sewing Machine Thread Bunching Up Here Why

Birds nest under the fabric big loops of thread top side looks good...

Fifth, when the upper thread appears on the underside of the fabric, the upper thread tension is too loose. If the bobbin thread appears on the top of the fabric, the tension thread is too tight (or the bobbin thread is loose). Start out with the upper tension set at the midway point and tweak it from that point. The tension is ideal when both upper and bobbin threads meet in the middle of the fabric.

Also, remember that tension is not static--a tension setting for chiffon will most likely not work on cotton or denim. Get comfortable adjusting the tension to suit the project you are sewing.

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You didn't explain the symptoms. Is the thread bunching, looping, knotting under the fabric? Is the bobbin thread rising to the top of the fabric?

If it is bunching under the fabric, it is probably what is called thread nesting or bird nesting. There are several fixes, sometimes more than one fix is required to resolve the issue.

Be sure to clean under the needle plate, around the bobbin, and the feed dogs. If the machine has instructions for oiling, follow the directions using a fresh, good quality sewing machine oil and apply only 1-2 drops each spot.

Install a brand new needle. Make sure you are using a needle compatible with the thread and fabric being used. All About Needles
Best practice is to use the same thread in both the upper and bobbin. Also, avoid old or bargain bin thread. Spend an extra couple of dollars to reduce frustration and increase success with your machine. If you wish, you may use two different colors of thread to test so you can easily determine what is happening with the tension.

Remove the thread from the machine. RAISE the presser foot and rethread from the beginning--the thread needs to be seated firmly in the tension disk. Verify that the correct thread path is followed (consult the owner's manual).

Set the upper tension to the midway point between high & low numbers (this is the factory standard and is a good place to start, but every machine is different and may need adjustment).

Confirm that the bobbin is installed in the bobbin case (turning the correct direction) and that the bobbin case is threaded properly.

Before beginning to stitch, hand rotate the handwheel one rotation and pull the bobbin thread to the top of the fabric. Then, gently hold the thread tails in the left hand and slowly begin to stitch.

Test.

If thread is bunching, looping under the fabric, the upper tension is too loose. Tighten it and retest. On most machines, the lower the tension number, the looser the tension.

If the bobbin thread is rising to the top of the fabric, the upper tension is too tight. Loosen the upper tension and retest.

Keep adjusting and testing until it is where you want it. Generally, tension is correct when both threads (upper & bobbin) meet in the middle of the fabric. FWIW, tension is static and should be tested and readjusted every time a new project is begun. The needle, thread, and fabric will affect the tension, so it is important to get comfortable adjusting the tension.

Also found the following reviews. Appears that some users have had tension issues with their CG550.

Amazon com Customer Reviews Singer CG 550 10 Stitch Commercial Grade...

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Are you 100% sure you are using the right size bobbin?

1. make sure your machine is threaded right.2. set the tension between 3 and 4 and play with the tension as you need it to adjust it.3. make sure the bobbin is threaded right.make sure to visit the site below; it has solutions to multiple problems and instructions how to thread the needle or bobbin. Good luck.htt://Fix Looping/Knotting Thread Fix Knotting/Bunching Thread Looping Bunching & Knotting Thread

Clean out the bobbin area if there are any thread tangles there.

Refer to the maintenance section of the manual - see the configuration of the bobbin case and shuttle race? The bobbin case as an extending arm and the race a notch. When inserting the bobbin case into the shuttle, turn the handwheel so the needle is at it's highest position. Then lift the lever on the back of the bobbin case and insert the cast into the shuttle, arm pointing straight up toward the bed of the sewing machine.

Now thread the machine with the presser foot up - always - and see if the tangling stops.

When you forget to lift the presser foot before threading the machine, the tension control does not open to capture the thread. Then when you begin to sew, the top thread has no tension, and the bobbin thread, which does have tension, pulls the top thread to the bottom in messy loops.

Change needle-flat side to the back of the machine
Clean under needle plate where feed dogs are for lint
Clean bobbin area for lint or loose threads
Rethread machine top thread make sure to get every thread guide
& make sure bobbin is wound correctly & that it is inserted correctly in the bobbin case or shuttle
Check tension 3 or 4 is usually good

with some machines the thread comes off the thread take up lever

1. Loosen needle screw & insert needle with shank's flat side facing front of machine. Push needle in all the way, then tighten screw to hold needle in place.
2. Install a fully wound bobbin by loosening bobbin nut & placing bobbin on top. Re-attach bobbin nut & tighten. If standard thread spool will be used, then attach spool pin to bobbin shaft & place thread spool onto shaft. Attach white spool cap on end of thread spool, then tighten. Bobbin/spool should unwind facing forward toward needle.
3. Bring end of thread through thread guides & over tension control. Pass end of thread through needle eye, from back to front, & pull it out about two inches.
4. A spring pushes pressor foot onto fabric that is being sewn, so lift pressor foot & place fabric underneath.
5. Turn large handwheel on side of machine (handwheel can be turned in either direction) to raise needle arm to its highest position.
6. Holding the Handy Stitch in place with your right hand, press on power switch & begin sewing. Guide fabric (being sewn) with your left hand.
7. To end this sewing session, turn off power. Turn handwheel to raise needle to its highest position. Carefully pull out about three inches of thread through needle & snip, then lift pressor foot to remove fabric. Turn fabric over & loop needle threader through last stitch. Place end of thread from underside through eye of needle threader, & pull to loop through. Pull to tighten and snip end of thread.

Sometimes even though the tension is at recommeded placement, you may find with various fabrics or threads, you have to adjust it. I would try to raise the tension just a bit. Try it a little at a time until you achieve a stitch you are happy with. If adjusting the tension does not correct the problem, double check your threading. If sure it is threaded properly, especially going through the tension assembly...check your thread. I have found that the thread you use can and often does create tension problems. Try changing the thread and see if the stitch quality improves.