Originally Posted by CaptMoto

Dear g-tec, the XT660X & R were put on the market in mid to late 2004, as you can see from the attached fax, the first batch of bikes came with a faulty ECU that fault was in the fuelling setting, most of these bikes had serious cut out issues at low rpm, hence Yamaha recognized the problem and offered a free ECU replacement to all owners. Supposedly all bikes built after 2005 should come with the new ECU, however we have heard stories of bikes built after '05 with the same problems which is why I have decided to post this message for owners.

The old saying: "if it ain't broke don't change it" means you are one of the lucky few so don't worry. or..... perhaps your bike was within the range and if you have bought it 2nd hand someone has already changed it or... Yamaha replaced it from the dealership before selling it to you. Open the right hand side panel under the seat that covers the air box and read the number on the ECU to see if its the new or old one.