As spaceclam said the higher end engines are great, but like NIK I also have an os 46la that does the same thing, I have plenty of experience with smaal engines, I set it, fly it & it will run great for 2-3 minutes. Then it will start slowing down, loosing power until it is a dead stik. I have tightened all the engine screws thinking I had crankcase pressure leaking or head leaking, made sure the carb was sealed good to the crank case. This engine has maybe 20 flights on it & I have tried every thing I can think of to make it run right to no avail. It ran good for about 12 flights & has been nothing but trouble since. I have quit trying & wrote it off as junk!!
Any Ideas???
Gil