Call your dearler an take it back. I have three janome's an never had a problem. There is definitly something wrong that needs to be fixed.

I bought a new 6600 and had to replace the foot pedal. I noticed the machine was slowing down, and it eventually stopped. I'd heard others on the Janome forum talk about having to replace the foot pedals. At least it was still under warranty, so I didn't have to pay for the new pedal. I also had a problem with the tension knob slipping all the time. I actually taped it in place to keep it from moving. I took it in and they tightened the knob. It's still a little loose, but it doesn't just slip on it's own. I would set it on 4, and the next thing I knew it had gone down to 0 all by itself. I don't know if your problem is the pedal, but you need to take your machine in and have them look at it.

Actually a friend of mine suggested the pedal too. Said she had had an incident where the pedal was bad. I would've never thought of that!! She let me borrow hers and I will try that as well as taking it in. Thanks for the feedback :0

If it is a short in the wiring where it is moving and coming separating it would happen anywhere. A small broken lead in the wire causes many problems. Please just go all over the wire and where it is wired into plug very carefully looking for a loose section or a split . If it is this it could cause a fire when shorting.
Coming from an electrical family if I miss this they are very short on helping. Just tighten the leads in the plug a little.

Definitely call the dealer. No machine should run like you described. Wishing you luck and getting to sew more :)

When I had to replace a foot pedal my dealer told me, "too bad, but the warranty only covers the actual motor--the motor, not the face plate, pedals, etc." (That's here in Poland.)

I went ahead and took it in to my dealer. They called today to say they ran diagnositics on it and he said he was able to get it to do the same thing that was happening to me. He called Janome who suggested that it "might" be the pedal. So they are replacing the pedal free and if that doesn't work we will try again. Hopefully this is it. I will updated. Thanks for all the responses :)

I am coming to this discussion very late. I have the Janome 6300 and never experienced this problem. Mine cruises along at top speed as long as I want it to, and sometimes it has more power than I do! :) I hope you got this machine back to the dealer for service! This sounds like a warranty fix and I hope you will love your machine in future! Could you update us on how it is doing? Wishing you the best!