I have a new P-90 RXi B It ran great for 3 runs / each only 5 minutes. Then it started to serge from 48,000 to 60,000 rpm at start up & I had no throttle control at all . Blue flame was shooting out the tail pipe as it accelerated each time. I would shut it down & try another start . I did 5 starts but every time it repeated this same problem I returned it to Dream Works . They said the new Brushless fuel pump was bad. I paid $250 just to get the better brushless fuel pump. Anyway I got it back & after another 5 runs each only 5 minutes it did the same thing. When it did run like it should it would not stabilize it between 45,000 & 60,000 rpm's. If you throttled below 45,000 rpm or above 60,000 rpm it's perfect.