@MeganMills Glad you've got it sorted. Some old machines can be slightly choosy at times but it's usually down to tolerances in my opinion. As for tension issues, I always start with setting the bottom tension, then move onto tweaking the top tension.
As for a noisy shuttle, I've had this before on the 400 series a few times and this has been down to wear. Metal parts do wear out and we never really know how much an old machine was once used. Again, glad it's sorted and happy sewing
In my experience, the 27's & 28's can be troublesome at times and that the improved 127/128 model is a better choice for using on a regular basis. Have had both machines