I also modified a hopping foot to glide on my Brother Innovis 4000D machine. I use both hopping and gliding, but I think I slightly prefer the gliding. Haven't had the types of issues you're describing.

I don't own a Janome 7700, but do have 8900 SE, and numerous other Janomes. I took the 8900 out of the box, didn't even change the factory needle. Looked up instructions in my book that came with the machine. Followed the directions, plugged my machine in and FMQ a small test sandwich. It was perfect, to my surprise. Then I took the same machine that weekend to a FMQ Bootcamp.....put in the needle the teacher told us to bring, threaded with beautiful new thread. OMG, immediately had issues with broken thread, eyelashes on the back, and then, a broken needle flying in my face. The teacher came over, she wouldn't figure it out.....then I turned my thread spool to the side and saw writing....it gave me a totally different needle size for that thread. Changed the needle and it worked perfectly. Needle and thread have to be compatible. Also, make sure your pressure foot bar is down! Another student had that issue. Gliding is good, but you still need some pressure....test that and the other issues mentioned, and try again. Also there is a Janome yahoo group for 7700.....members love to share information

I have had a 7700 for at least 6 years. I haven't had any similar problems, sorry, so I'm not sure if I can help. I will say that right out of the box, my quilting looked pretty good without changing anything (but my quilting level is intermediate, at best). I have had the best results using a poly thread (Isacord, Glide, etc.) in the top thread and Bottom Line or So Fine in the bobbin. Adjusting the foot height, especially if I had bulky seems, made a difference. I use Organ needles, because I believe they also manufacture the Janome needles, and I get good results with them. The best thing I did was to use the insulation foam to build up the area around my machine. I used duct tape to edge the foam, and covered it with vinyl from Walmart. I did buy the blue dot bobbin case, which I have never felt the need to use, so that was a waste of money for me. Good luck with your machine. I absolutely love mine.

I can't really say that I've seen that much difference between a hopping foot and a gliding foot, though I haven't used a Janome. Loops on the bottom could be from a variety of causes. The first thing I'd try is put on a regular or zigzag foot and try sewing a line on a scrap of fabric. If it's still making loops, that would rule out your quilting foot as a source of difficulty. Maybe the bobbin thread missed the tension? Sometimes my machines will do that sort of thing only because there is lint under the bobbin case. Recently I had similar problems that turned out to be caused by a rough spot on the edge of a plastic bobbin. The thread would catch on it and then pull loose, and of course that varying stress broke the upper thread several times before I figured out the cause.

I have a Janome 9400. I use a purple tip needle and single hole throat plate , gloves, and the blue dot bobbin case for fmq. I much prefer the gliding foot to the hopping foot. My machine has an fmq setting that automatically puts the foot at the correct height. I don’t know if your machine model does that. My Pfaff QE 4.0 that I used prior to my Janome had both gliding and hopping and I didn’t like the hopping foot.

I’m sure you know this, but it’s important that there is no pull on your quilt .

As Watson mentioned I think you get smooth curves with the gliding foot.

I teach fmq on domestic while in Fla. in winter. My students bring their machines, so l notice the different feet and machine combos. Most do way better with a hopping foot...but when it comes to ruler work, they need to learn to use gliders. There's often 1 or 2 machines that have issues ( including my own Janome 6500. Oddly enough, my 8900 Horizon does well!) The main reason, l believe, is the height adjustment.Set it too high and it skips, too low and it " grabs" the sandwich. Often , l find a nice height, only to get hung up on seam intersections. I suggest you stick with a hopper, as it helps with the rhythm of the machine while stitching. By the time you're ready for ruler work on your new machine, you will have become more familiar and comfortable with it, thus giving you confidence. You likely already know how important managing the quilt is while doing fmq, as you've been at it a while...but it wouldn't hurt to set your ironingboard or low table to your left to keep the quilt from dragging up from your lap.

Wow... I had the exact opposite experience to you. I loooove my gliding foot! I can finally get consistent stitch length and smooth lines. I'm sorry yours is giving you trouble.