If the clutch shoe spring is broken, the clutch will try to engage and drive the model while the engine is starting. Remove the metal clutch bell gear (to remove clutch bell gear, follow steps 1-3 here) to examine the clutch shoes and the spring. If necessary, replace the spring. On Revo, T-Maxx, and Nitro Stampede, the engine will need to be removed. On Nitro 4-Tec and Nitro 4-Tec Pro, Nitro Rustler, Nitro Sport, and Jato the engine can stay in the model.