I had a similar problem with my ng460. It was due to the choke mechanism and spring being broken. The choke was earthing to the mower body causing the engine to splutter/cut out/not restart. I took it apart and reset it back to where it should be and it seemed to sort the problem. If this is your issue, keep an eye on it though - mine went wrong again after about 6 months and i had to go through the same procedure again.
Good luck
Ricky B, May 2008
