I have a 1600P model. I just came back from the Janome dealer where I picked up some purple tip needles because I was having a problem with skipping stitches and breaking thread. Along with the purple tip needles, I picked up a package of high speed needles as well as a new darning foot that has a screw on top to adjust the height of the foot.
I guess I'm assuming that your skipped stiches are when you are FMQ. Maybe your machine came with this newer darning foot, mine is older so......
I'm attaching a link so that you can see the difference between what you might have on hand. Keep in mind that this foot is the 1600 model but you can inquire to see if they make one for your 8900.
http://www.ebay.com/itm/Janome-Darni...-/181838500325