he is correct, traxxas fuel has alot of oil and the sh engines have an internal one way, the traxxas fuel will make the one way bearing start to slip. you have to take the backplate off, get to the bearing and spray it down with some carb cleaner or brake cleaner, let it dry and re install it. Bryrons, odonells, trinity are good fuels, most fuels are good and traxxas is good to but not for engienes with internal one way bearings.