You either understood it wrong or they lied to you. It doesn't matter if you run synthetic or conventional or blend, it's the ratio and quality, and what octane you're running to match your engine mods. And there's no, absolutely no reason to clean the engine out when using a different type of oil, unless there's excessive carbon buildup on the head/piston top, but that would be really unlikely after only 25 hours. I'll avoid the obvious reason that your kx died(cause it's a kx), and point out that dying in the air is USUALLY caused by improper carb adjustment and not having it vented properly. Few dirt bikes come with the carb vented right from the factory and it can cause them to die after lift off or impact. And why on earth would you let a foul-proned 2 stroke warm up for 10 minutes?!
