Hey 2004. I had the same problem In a way. I have the Fox 2.4 with a 20x10 xoar on an extra Klotz 40:1. This motor ran great never let me down. Not one deadstick in over 200 flights. Well Motorsports shop stoped carrying klotz. Talked around an ordered some Amsoil Saber.Mixed it 40:1 went to the field an re-tooned.Ran OK on the ground 6800rpms. Which was about 1000 less than what I had been getting. Took off an it had a burbble that was holding it back, Throttle response was normal, just lots of burbbles. Finally the first of 4 deadsticks all within 3 hours.....So I started talking to everyone asking If they had anyIdeas.Nothing.....So I went home an started reading....Not trying to start an oil war here but what I found was there are some oils that don't work well mixed at real rich ratio's.Like Saber.Now I was one of those guys who said 40:1 is a lean as I will go cause I want my engine to have some oil. Well after reading about how to much oil creats carbon behind the ring an on the piston, I started trying new mixs. Weedeater is my test bed. It was turning 6100 on 40:1 Saber. So I tryed 60:1 an it jumped to 6980. Tryed 75:1 an it turned 7300. Its a really old Ryan with the ryobi engine.....I weedeated the yard, almost a mile of fence line, then went behind the barn an ripped into black berry vines. About 6 hours of weedeating. As the day went on an I worked deeper into that 2 gallon gas can it was running better an better.All the oil on the muffler was gone,The spark plug that was always black an gummy was turning a light brown. It was starting better aswell..... I work out of town so when I was gone my wife called an asked if I had rebuilt the weedeater cause it started in 4 pulls an not 9. After getting back home I looked the piston an plug over in the weedeater. Finally I worked up the nerve to try the 75:1 in my model. It started better, I tooned it an got 7730 out of it. It does not burbble at all an has never tryed to stop in the air on me agin. I have 4.5 gallons ran throgh it sense the day of the deadsticks.......Runs better than ever............Take what you want from this. Maybe it will help