Check： If the the tension of the needle thread too much or too little?
Adjustment： Adjust the tension of the needle thread
Check： The right looper didn’t hook the left looper thread while they are crossing each other?
Adjustment： Change the new left looper. (The top of the left looper is worn. When fix and replace, the protrusion of the looper top shall not be worn.
Check： Is the upper thread tension too weak, or is the looper tension too strong?
Adjustment： Adjust the upper thread tension or looper thread tension.
Check： Is the looper thread tension too weak, or is the upper thread tension too strong?
Adjustment： Adjust the looper thread tension or upper thread tension.
Check： Is the sewing speed setting or backtack speed setting incorrect?
Adjustment： Use the sewing speed control keys to set the high speed.
Check： The space between the right looper and needle is too wide?
Adjustment： When the right looper turn right and backward, the distance to the needle has to be 0.1 mm, which is using the correct right looper. (The appropriate right looper for each type, such as single need, 2 needles, materials, and thin fabrics, are included)
Check： The distance is too wide between the right and left needle when using 2 needles?
Adjustment： Because the correlationship of the left/right position of the right looper while assembling and the up/down moving position of the right looper seat, adjust the movement path of the looper. When the right looper descends, decrease the descending amount from left needle to right needle.
Check： Is the power supply connector disconnected from the control box?
Adjustment： Insert the connector securely.
Check： Choose the wrong needle?
Adjustment： Please select the needle and the thread number that are suitable for the sewing materials.
Check： Bad needle?
Adjustment： Change a new needle.
Check： A clearance exists between the needle and the left looper tip?
Adjustment： Adjust the clearance between the needle and the left looper tip to be ±0 mm.
Check： Does the small tension adjusting spring not function?
Adjustment： (1) When the small spring doesn’t function, pull the spring a little to give it more tension. (NOTE: The thread will be broken if pulling the spring too much.)
(2) If there is any groove or deep scrape on the tension adjusting disc, please change a new adjusting disc.。
Check： Is the needle thread too tensed?
Adjustment： (1) Loosen all the needle thread tension a little.
(2) Adjust the line (A) of the needle thread to the highest position, so that the released amount of the needle thread from thread hooking will decrease.
(3) Lean the line (C) to left a little to increase the released amount of the looper thread.
Check： Is the material being pushed or pulled with excessive force during sewing?
Check： Is the needle properly installed?
Adjustment： If it is incorrect, install the needle correctly.
Check： Is the needle bent, is the needle tip broken, or is the needle hole blocked?
Adjustment： Change a new needle.
Check： It is extremely dangerous to leave any pieces of broken needle sticking inside the material.
Adjustment： If the needle breaks, search for all pieces until the whole of the needle is found.
Check： The right looper and the needle have wrong height position?
Adjustment： When the needle moves close to the upper dead point, push the needle forwards a little by finger. See whether the top of the needle touches the right looper or not. Then adjust the height of the needle position or the moving position of the right looper.
Check： Is the needle guard too close?
Adjustment： The needle guard inside must leave from the needle before the top of the left looper reaches the right side of the needle. The distance between the front needle guard to the needle is about 0.2 mm.
Check： Incorrect needle plate assembling position?
Adjustment： When assembling the needle plate, pull it forwards a little so that the space of part A can be larger.
Check： The thread hole of the thread stand did not polish?
Adjustment： Use emery cloth to polish the surroundings of the thread hole.
Check： Choose the wrong thread?
Adjustment： Change a better thread to balance the threads.
Check： Is the fixed stitch key turned on?
Adjustment： Use the sewing speed control keys to set the high speed.
Check： Is the power supply voltage too low?
Adjustment： Check the power supply. (If the power cord is too long or too many appliances are being run from a single outlet, this may cause voltage drops.)
Check： The cam of the chainstitch looper is not appropriate?
Adjustment： Adjust the cam to an appropriate position.
Check： Thread tension device does not work well?
Adjustment： (1) Adjust the spring strength (2) Polishing or changing a new one
Check： The presser foot rear spring was not assembled well?
Adjustment： Readjust the spring or change a new one to make sure the presser foot can act smoothly and test its pressure.
Check： The eccentric is rusty?
Adjustment： Clean the stuck part so that the oil can reach the cam.
Check： Inappropriate adjustment of the eccentric cam control spring?
Adjustment： Adjust to the proper tension, but should not be too loose.
Check： The oil does not come out from the pump?
Adjustment： (1) Relock it to the correct position (2) Reassemble the gear of the pump to the main shaft and adjust the position.
Check： Upper mechanism does not splash the oil?
Adjustment： (1) Clean the lints and change the oil releasing screw.
(2) Change a new filter
(3) Clean the dirt or change a new one
(4) Use the iron wire to clean through the oil path.
Check： The main shaft is loose and has noise?
Adjustment： Clean the copper glue from the copper cover of the main shaft and readjust.
Check： Noise of the pump (scratchy?)
Adjustment： Use the fixture to add pressure on the gear of the pump, and keep the pump running 3-5 minutes.
Check： The needle bar is loosening?
Adjustment： Change a new one or to polish the contacting surface so that the clearance is smaller.
Check： Noise from the belt wheel?
Adjustment： Adjust it based on the norm.
Check： Is the needle tip bent? Is the needle tip blunt?
Adjustment： If the needle tip is bent or broken, replace it.
Check： Is the needle properly installed?
Adjustment： If it is incorrect, install the needle correctly.
Check： Is the machine properly threaded?
Adjustment： If it is incorrect, thread the thread correctly
Check： Is the presser foot pressure too weak?
Adjustment： Adjust the presser foot pressure.
Check： Is the needle too thin?
Adjustment： Replace the needle with a needle that is one rank thicker
Check： Is the presser foot too high?
Adjustment： Adjust the height of the presser foot.
Check： Is the thread take-up spring too weak?
Adjustment： Adjust the tension of the thread take-up spring.
Check： Is the thread take up spring tension too strong?
Adjustment： Reduce the tension of the thread take-up spring.
Check： Is the thread take-up spring operating range too large?
Adjustment： Lower the position of the thread take-up spring.
Check： Are the trailing lengths of the upper threads too short after thread trimming?
Adjustment： Adjust the tension
Check： Are the threads not being trimmed cleanly?
Adjustment： Sharpen the fixed knives, or replace the fixed and moveable knives if necessary.
Check： Is the needle too wide?
Adjustment： Try to use a needle with a count that is one lower than the current needle.
Check： Is the sewing speed too fast at the sewing start?
Adjustment： Use the slow start feature.
Check： Is the presser foot pressure too weak?
Adjustment： Adjust the presser foot pressure.
Check： Is the feed dog too low?
Adjustment： Adjust the feed dog height.
Check： Is the needle thread tension too strong?
Adjustment： Make the needle thread tension as weak as possible.
Check： Is the looper thread tension too strong?
Adjustment： Make the looper thread tension as weak as possible.
Check： Are the thread take-up spring tensions too strong?
Adjustment： Make the thread take-up spring tension as weak as possible.
Check： Is the thread take-up spring operating range too large?
Adjustment： Lower the thread take-up spring as low as possible..
Check： Is the presser foot pressure too strong?
Adjustment： Adjust the presser foot pressure.
Check： Is the sewing speed too fast?
Adjustment： Use the sewing speed control keys to gradually reduce the sewing speed.