When a motorcycle runs out of fuel completely, it can be challenging to start it again due to a few reasons:
Air in the Fuel System: When a motorcycle runs out of fuel, the fuel lines, fuel pump, and carburetors (if equipped) may become filled with air instead of fuel. Air pockets in the fuel system disrupt the normal flow of fuel and prevent the engine from receiving an adequate fuel supply. It takes some time and effort to purge the air from the fuel system and re-establish a continuous flow of fuel to enable proper engine starting.
Loss of Fuel Prime: Many motorcycles rely on gravity or a fuel pump to deliver fuel from the tank to the engine. When the fuel level drops too low or runs out completely, the fuel pump loses its prime, meaning it can no longer effectively pull fuel from the tank. Restoring the fuel prime can take some time and effort, as the pump needs to re-establish suction and draw fuel into the system.
Vapor Lock: In some cases, when a motorcycle runs out of fuel, the residual heat in the engine and fuel system can cause the remaining fuel to evaporate or vaporize. This can create a vapor lock situation where the vaporized fuel disrupts the normal fuel flow and prevents proper starting. It may require some cooling time or additional measures to dissipate the vapor and allow for proper fuel flow.
Carburetor Issues (if equipped): Older motorcycles or certain models may have carburetors instead of fuel injection systems. Carburetors rely on a precise balance of fuel and air to function correctly. When a motorcycle runs out of fuel, the fuel-air mixture in the carburetor becomes imbalanced or depleted, making it difficult to achieve the optimal fuel mixture for starting.
To address these challenges and start a motorcycle after it runs out of fuel, it is advisable to follow the manufacturer's guidelines, which often include the following steps:
Refuel: Ensure the motorcycle is properly refueled with an adequate amount of fuel.
Prime the Fuel System: Depending on the motorcycle model, there may be a specific procedure to prime the fuel system and purge air pockets. This typically involves turning on the ignition, waiting for the fuel pump to cycle or manually operating the fuel pump (if applicable), and repeating the process several times to restore fuel flow.
Cool Down (if vapor lock occurs): If vapor lock is suspected, it may be necessary to allow the motorcycle to cool down for a period of time. This allows the vaporized fuel to dissipate, reducing the chances of fuel flow interruption during starting attempts.
Follow Starting Procedure: Once the fuel system has been primed and any necessary cooling time has passed, follow the standard starting procedure for your motorcycle model. This usually involves engaging the ignition, activating the choke (if applicable), and using the appropriate starting technique (e.g., kick-starting or using the electric starter).
It's worth noting that modern motorcycles with fuel injection systems generally have better fuel management and are less prone to starting difficulties after running out of fuel, compared to older carbureted models.