A needle jam can cause a timing issue, it can also bend a shaft slightly if the needle hit the plate or bobbin case....did it break the needle? I would trade it in on the 8900. I love my 8900. I have a 6600 that is also a great machine. I wasn't the best FMQ'r when going around curves....I got the 8900 for the extra harp space, BEAUTIFUL decoratibe stitching since it is a 9mm machine, and guess what....Right out of the box, I decided to go for FMQ. Looked in the instruction book....set the machine, no tweaking, no special thread, started FMQ...lots of curves, Turned it over NO EYELASHES. It is great for piecing and free motion...I love this machine so much, I purchased a second one for the cabin.....Oh, I had a problem with the Accufeed FOOT,,,...NOT THE MACHINE. The foot is what the problem was with this machine...my dealer sent me a new one free of charge. No problems since. I think the ones coming with the machine from the factory, or at least some of them had feet with plastic that either broke or would not stay in place.
This machine is perfect, at least for me. If you have any questions, go to the Janome 8900 group. I used to belong to the Janome 7700/8900 group. Too many issues being talked about the 7700, so an 8900 group was formed. I have yet to see a machine problem on this yahoo group. That should say something about this machine. Best wishes in your quest.