A two-stroke outboard motor is popular due to its simple design and high power-to-weight ratio. This design, however, requires a specific starting procedure, especially when the engine is cold, to ensure proper fuel delivery and lubrication. This guide provides a clear, safe, and effective method for starting a carbureted two-stroke outboard, helping to maintain engine health and reliability.
Essential Pre-Start Preparation
The longevity of a two-stroke engine depends on the correct fuel mixture, as it lacks an internal oil reservoir and relies on oil mixed with gasoline for lubrication. Most modern outboards require a 50:1 ratio of gasoline to oil, though some older models may use 100:1 or 25:1 ratios. Using manufacturer-specified TCW3-certified oil is necessary to prevent premature wear on internal components like piston rings and bearings.
Before starting, the safety lanyard (kill switch clip) must be securely attached to the operator and the engine. This ensures the motor shuts off immediately in an emergency. The engine must also be submerged in water or connected to a flushing device, such as muffs, to supply cooling water to the impeller. Running the engine dry for even a short time can cause severe damage. The gear selector must be confirmed to be in the Neutral position to prevent the propeller from spinning upon ignition.
Fuel must be delivered to the carburetor before starting. Locate the primer bulb on the fuel line and squeeze it repeatedly until it feels firm to the touch. This action pressurizes the fuel system and fills the carburetor float bowls, ensuring a ready supply of fuel for the initial combustion cycle. If the bulb does not firm up, the fuel tank vent may be closed, or the fuel line may be kinked, preventing proper flow.
Step-by-Step Cold Start Procedure
A cold engine requires a richer fuel-to-air mixture to compensate for fuel condensing on cold internal surfaces. This is achieved by engaging the choke mechanism. For most outboards, this means pulling the choke knob out fully or pushing the ignition key in while turning it to the start position on electric-start models. Simultaneously, the throttle should be advanced slightly (typically one-third to two-thirds open) or by using the fast idle lever.
With the choke engaged and the throttle set, perform the starting action by turning the ignition key or pulling the starter cord. When using a manual pull cord, use a slow, steady pull first to engage the flywheel. Follow this with a quick, smooth, and full pull to generate the necessary speed for ignition. The engine should fire quickly, often running roughly due to the overly rich mixture provided by the choke.
The choke must be disengaged immediately once the engine fires and begins to run, even if it is running poorly. This prevents the engine from flooding with excess fuel. If the engine stalls after the initial fire, the choke can be briefly re-engaged, or “bumped,” for a second or two before attempting another start. Once the engine is running consistently, allow it to warm up at a fast idle for 30 to 60 seconds.
A warm start is performed when the engine has run recently, meaning the components are already warm and the fuel has not condensed. In this scenario, the choke should not be used at all. The throttle should only be advanced minimally, if at all, to prevent flooding the engine. If the engine fails to start after a few attempts, wait a few minutes before trying again to allow any excess fuel to evaporate.
Troubleshooting When the Motor Won’t Start
A common reason a two-stroke motor fails to start is a flooded engine. This occurs when too much fuel enters the combustion chamber, washing away the oil film and preventing ignition. A strong smell of gasoline or a wet spark plug indicates this condition. To clear a flooded engine, move the throttle to the wide-open position, ensure the choke is off, and crank or pull the engine several times. This draws maximum air through the carburetor to expel the excess fuel from the cylinders.
If the engine cranks but shows no sign of ignition, the issue may be a lack of spark. First, ensure the safety lanyard is properly seated, as this is a common oversight. Another possibility is a fuel delivery problem, diagnosed by checking the fuel line for kinks or confirming the fuel tank vent is open. A closed vent creates a vacuum in the tank, preventing fuel flow.
A more serious mechanical issue is a sheared flywheel key. This small piece of soft metal aligns the flywheel to the crankshaft to ensure correct ignition timing. If the engine experiences a sudden stop or impact, the key can shear, causing the flywheel to rotate out of sync with the piston. The symptom is often an engine that cranks normally but will not fire, or one that backfires violently.