Introducing our high inertia coupler for the Yamaha 62t engine 63m and 65u engines . At first you are thinking it will make the engine respond slower, But what it actually does is smooth the power out and allow for better hole shots and hook up. There is a reason that the four strokes are faster on the track and one of the reasons is the way the power is delivered. While this doesn't bridge the gap to the four stroke power delivery, it goes a long way towards it. We have also found a good 1mph gain in top speed with these. Motor bikes guys have been doing this for years and now we are offering it to the watercraft industry. If you are running a sports spec blaster and find your self being out driven on the straights by another blaster then ask to see their coupler. We are working on ones for the Kawasaki x2 right now as well as other models. This uses the Kawasaki style drive rubber and comes with the engine side only.