I've got the same problem! I have a janome 1600p as well. I cleaned my rails and wheels and made sure all my wires and connections with the regulator were all good etc...my very first quilt was terrible, I ended up having many long dates with my seam ripper and soo many headaches...it has gotten better after I unplugged everything! and hooked it all back up...I put my regulator on 9 the highest it can go. I will get long stitches if I go to fast, I like to cruise along meandering and if I go to fast my regulator can't keep up with me, and if I go way too slow I get long stitches too, soooo I have to find my perfect speed and keep going. I put in a new needle because I broke it because it slowed down on me unexpectedly I was lucky I didn't tear my fabric! grrr...but yes I took it all apart and put it back together, new needle, cleaned my rails and made sure my wheels touched nicely and its seems to be better if I find that perfect motion...I wish it worked better though, I wish it could keep up with whatever speed I want to go for the price of that thing! anyway hope this helps a little, it seems we all are having about the same troubles.