The thread Must go over the bar (thread guard) before engaging the take-up spring. Here's what I see as a potential problem. The take-up spring in your first pic is limited in travel, and consequently tension. Notice how yours exits the tension assembly somewhere around 2:30 o'clock? The pic of the Juki built clone shows the take-up spring at about 4:00 o'clock. More travel means it will remove more slack from the thread.
Loosen the set screw for the tension assembly and spin it clockwise. It will only spin within the slot provided. If more is required you may have to do a little bending of the take-up spring, or check the correctness of the tension assembly. Those springs are fairly fragile and can bend easily if not threaded correctly.
BTW- Love the 41 Mercury in your avatar. Takes me back to my HS years. My nicest car was a 41 Merc coupe. Wish I still had it!
Last edited by QuiltnNan; 04-15-2019 at 07:43 AM.
Reason: shouting/all caps