Tension setting for a 70 weight thread
What tension should I be using on a Juki 98Q with 70 weight thread?
I wish I could tell you the exact tension setting, but you will need to create a practice quilt sandwich from the scraps leftover from your quilt--use a scrap of the same batting, too--and then quilt a bit on it. Check to see that the bobbin thread isn't showing on the top and the needle thread isn't showing on the backside. This practice sandwich doesn't have to be big or pretty or even square, but it is the best way I know to determine the correct setting.
If you're using the same thread in both the needle and bobbin, I suspect that you'll need to tighten up or increase the tension a smidgen because the thread is finer than that which your sewing machine is preset for at the factory.
The weight of your fabric and batting will both effect the tension, too, as they cause a bit of drag on the thread as it passes through the layers.
Adjust your tension and then test on your practice sandwich. Stop and evaluate your stitches. Repeat until you are satisfied.
Another benefit from doing this is you'll see exactly how your threads look stitched up. They may look different that what you expected from looking at it on the spool.
I wish I could offer more specific help, but this will get you to the perfect setting for your project.
Readers, if you own a Juki 98Q and can offer suggestions about its tension settings, please do share your thoughts using the 'comments' link found just below.