To access the carburetor, the throttle cable must be routed through the engine front panel and the cooling housing. In older engines, this tube is equipped with a spring system that ensures the throttle lever is pulled back. Later on, this was simplified by attaching a return spring directly to the carburetor. The pass-through tube is often bent or heavily rusted, which can cause the throttle cable to be damaged and break. The spring system for older engines is also usually so rusted that the throttle cable is no longer pulled back correctly.