I have a recurring problem with my Toro 6500. The mower runs fine for a while then all of a sudden loses power and splutters for a few seconds, it then picks up again and runs fine until the next splutter. This problem occurs when in transport and when there is load on the engine. Fuel and air filters have been changed and a new fuel pump fitted. I have also bypassed the seat switch to check if that is the problem. Has anyone experienced similar problems with this machine? Any advice would be much appreciated.