Black & decker LST201 direction loading the string weed eater

Be sure to install a brand new needle and that it is facing the correct direction.
Remove the top thread from the machine.
ALWAYS RAISE the presser foot and rethread from the beginning. Verify the thread path is correct.
Set the tgp tension to the midway point.

Verify the bobbin is loaded and thread correctly.

AVOID old or bargain bin threads.

not sure if this link will help you out. Sewing Lesson 10 How to Fix Tension on Your Sewing Machine

Search for:

Make Model manual

Make Model threading

https://www.youtube.com/watch?v=UzSCOC5AqVg

http://possumjimandelizabeth.com/xhtml/collect_sewing_weed.html

http://www.needlebar.org/cm/thumbnails.php?album=294

https://books.google.com/books?id=9H3tHKUFcfsC&pg=PA193&lpg=PA193&dq=Weed+sewing+machine+threading&source=bl&ots=lUI3tU1KbY&sig=OVDmRIfNzW9O6FzYM8ORt_ktUIo&hl=en&sa=X&ved=0ahUKEwiU4K6UyozWAhUV9WMKHevIBfEQ6AEIXDAN#v=onepage&q=Weed%20sewing%20machine%20threading&f=false

https://www.youtube.com/watch?v=ct9ZUyUmi1I

Since it is an early mechanical machine, it most likely would benefit having some nice oil (or Tri-Flow Synthetic Lube) applied every place that metal rubs against metal. Avoid any rubber or leather parts.

Remove the thread from the machine.
Install a brand new needle.
RAISE the presser foot and rethread the top thread.
Verify the thread path is correct.
Load and thread the bobbin case & install it. Verify it is correct.
Set the top tension at the midway point.
Re-test your stitch.

Sewing Machine Problem 1 Thread Breakage

10 reasons for skipped stitches

Watch your thread while sewing slowly. You may be able to see where the problem originates. It may just be a matter of the thread popping out of a thread guide or looping around something it shouldn't.

Avoid old or bargain bin variety thread. Invest in fresh, good quality thread.

Try installing a brand new needle.

When threading the upper thread, ALWAYS RAISE the presser foot. Remove all the thread from the machine and rethread from the beginning. Confirm the thread path is correct and that the bobbin is loaded and threaded correctly. Set the tension to the midway point to start and then tweak it for your particular machine.

Sewing Machine Problem 1 Thread Breakage

Why Does My Thread Keep Breaking While Sew

Sewing Machine Thread Keeps Breaking

Hi,
Try to go for a regular maintenance. Here i have added a video which will help you to carry out the maintenance process. Hope after that you problem will be solved.
SINGER Sewing Machine Maintenance Troubleshooting
www.electro-medical.blogspot.com

try changing the needles, also try adjusting the tension, make sure it's threaded correctly

Could be a timing issue. Is your machine a top load rotary , or a front load oscillating system, (ie. metal bobin case you put bobbin into then insert to machine, or black plastic bobbin case you "drop" your bobbin into...?

Sewing Tech

try this link for a free manual just in case you don't have one
http://www.singerco.com/uploads/download/36952a1312a6d8436174ef874f3662471a946b64.pdf
if the fabric is real light weight you may have to use a stablizer
also check to make sure the needle is the right one for the fabric being sewed..
make sure the bobbin is turned the correct direction, try putting the bobbin in the opposite direction..
if the machine keeps jamming, take it back up where you bought it and show them what it's doing and see if they can help you..

It sounds like the needleis not installed correctly, check the manual for the proper instructions.