Maybe I should change chains, but right now I would like to align the engine sprocket with the rear wheel sprocket so the dang chain will stay on. I'm going without an idler, as I do on my other bike. I didn't have this problem on my first bike, the chain stays on fine. On the present bike the chain comes off the bottom of the rear wheel sprocket, to the inside. I've moved the wheel around, changed the angle of the engine, all without success. Now I'm wondering about trying to put an unequal number of washers in the rear motor mount. What do you guys think? I need help.