I have about 60 hours on mine. I had to switch to a hotter spark plug to eliminate an idling problem. Other than using a lot of fuel over 4,000 rpm, they are great! If I had to do it over again, I would have chosen the 525's. They run almost as fast, use less fuel, cost a lot less, have closed cooling, and no blowers to maintain. I am still trying different props to get the max rpm and speed. By the way, the sound of these motors may be worth the price!