some or all of these are tips you have probably already tried.
i repeat them because others with Horizon models might benefit.
they are not "professional" recommendations - just things that always worked for me on my MC8900 (a Horizon model.)
double check to make sure you have lowered the feed dogs.
it's good that you started with a test sample.
that's only part of it, though, because our quilts will be larger and heavier.
that will make a big difference.
skipped stitches might mean there's too much weight and/or drag as the quilt travels over the machine bed.
are you using the extension table?
they are quite pricey but worth every penny - especially during free-motion.
On Horizon models, Organ brand needles are a "must" for free-motion. (the good news is that they cost less than most other brands. I buy mine in bulk from CTSUSA.com) (Janome branded needles are actually Organ brand that have been color coded and brand-packaged at a significantly higher price.)
a fairly safe size to start with is a size 14. rarely i'll need to go up to a 16.
use this free-motion foot (if you don't have one, shop around because prices vary widely online):
https://www.janome.com/accessories/s...e-freemotion-/
it makes such a difference I ordered one for my brother dream machine2.
using the adjustment screw on the foot assembly, try adjusting the foot height. i start with the foot all the way down. that's usually good but i'll occasionally need to heighten it. (if i remember correctly you can also tweak the foot height even more in the machine settings.)
set the tension to the maximum.
size 15/A bobbins - always.
i have the best results using prewound bobbins. they are usually 60wt. cotton when i could use neutral colors ... polyester if necessary to get the right color in the bobbin.
i never needed the special bobbin case on my MC8900 but it won't hurt anything if you want to try one. they are not horrifically expensive.
i know that nearly everybody holds their hands flat on the quilt as they move it around.
that works for nearly everybody, but i could never get the hang of it on any machine i have ever used.
instead of keeping the quilt flat to the machine bed, i lift it a bit to eliminate as much weight and drag as possible.
sometimes i have both hands under the quilt holding bunches to the side; sometimes only the left is under while i use my right to bunch from the top; sometimes both hands are bunching from the top.
even when i'm using my Martelli brand circular free-motion weights i don't press down. i put my hands under the quilt and bunch a bit over the top of each handle.
all very weird, i know. i keep trying to do it the traditional way, and maybe someday i will succeed. but - so far - i always end up reverting to lift methods instead of "press down" methods.
if all this blabbering wasted your time, i apologize.