Here is an easy thing to check, it happened to me once and I thought the engine was going crazy after being real stable. Check to see if the needle vavle turns too easily if so it might just be turning from vibration. just remove the valve and bend that little tab (the one that makes the click noise) in a little and then screw the needle valve back in. Hope this makes sense, I know it seems very basic and don't want to insult you if you already thought of this. Good luck