The outboard will not start: causes and what to do

An outboard that refuses to start spoils a day out, and sometimes more when you are already on the water. The good news: most starting failures have a simple cause, which you find by checking things in order. This guide covers petrol outboards, two-stroke or four-stroke, with pull or electric start. For an inboard engine, see the boat engine will not start instead. Your engine manufacturer’s manual always has the last word, especially for the cold-start procedure, the oil mix of a two-stroke and the approved fuel.

1. What you notice

• With the electric starter, nothing happens, or just a “click”.
• The starter turns slowly, weaker and weaker.
• The engine turns over with the pull cord or the starter, but does not catch, no firing at all.
• It starts and then stalls straight away, or as soon as the choke is released.
• The pull-cord handle is stuck or will not pull.
• It coughs, will not hold idle, smells strongly of petrol.

2. Safety first

Petrol and its vapours ignite very easily. Do not smoke, keep any flame away and air the space if a smell of petrol persists, especially in a locker or under a closed cover. Wipe up any spilt petrol before starting the engine. Before starting, check that nobody is near the propeller and that the engine is in neutral. Never run an outboard out of the water without the flushing device the manufacturer specifies (muffs or tank): its water pump, cooled by the water it draws in, is damaged within seconds when dry. Before touching the spark plugs or the electrical circuit, remove the kill-switch key and disconnect the battery. Many manufacturers advise against “starting aid” sprays: use them only if your manual allows it. Finally, if you are already on the water and the engine will not restart, think of the boat first: anchor if the bottom allows, or call for help before you drift onto the shore.

3. Likely causes, from most to least common

• Kill switch missing or not properly fitted — the red lanyard attached to the helmsman (the “dead man’s switch”) cuts the ignition when its key is pulled out. Key not pushed fully home, lanyard torn or switch corroded: the engine turns over but never starts. This is the first thing to check.
• Not in neutral — most outboards refuse to start in gear, for safety. A badly adjusted remote control can make the engine think it is in gear when it is not.
• Fuel missing, stale or mixed with water — petrol ages within a few months, especially petrol containing ethanol, which attracts moisture. After a winter, this is one of the most common causes. On a premix two-stroke, the wrong oil ratio also makes starting harder.
• Tank vent closed — a portable tank has a small vent screw or cap. Closed, fuel no longer flows: the engine sometimes starts, then stalls after a few minutes.
• Primer bulb or connectors — the bulb should become firm after a few squeezes. If it stays soft, collapses or does not fill, the bulb, its valves, the hose or the quick connectors (engine and tank side) are letting air in.
• Choke used wrongly or engine flooded — when cold, most carburettor engines need the choke; when warm, it floods them. Too much fuel in the cylinders and the plugs are wet: strong smell, no start.
• Weak battery or corroded connections — for electric start: slow starter, a single “click”, dimming lights. The boat’s terminals, often wet, corrode quickly.
• Fouled or worn spark plugs — black and wet, covered in deposits, or with too wide a gap. A plug cap that is not pushed on properly has the same effect.
• Blocked fuel filter or water separator, water in the fuel — many outboards have a small visible filter under the cowling; some boats also have a water-separating filter. Water or deposits at the bottom of the bowl: that is where the fault is.
• Gummed-up carburettor or injection — petrol left in a carburettor evaporates and leaves a varnish that blocks the jets. Typical after a winter lay-up without preparation.
• Stuck pull cord — a handle that will not pull may come from the starter pawl, but also from the engine itself being locked (water in a cylinder, internal damage): in that case, do not force it.
• Ignition or sensor fault — coil, electronic module, wiring: rarer, and a workshop diagnosis.

4. What you can check yourself, safely

• The kill switch is properly in place, key pushed fully home, lanyard intact.
• The control is in neutral; on a remote control, try moving it slightly around neutral.
• There is fuel, the tank vent is open and the fuel tap (if there is one) is open.
• The hose quick connectors are properly clicked in on the engine and tank side, and the bulb becomes firm after a few squeezes.
• You follow the starting procedure in the manual: choke only when cold, throttle in the position indicated.
• If the smell of petrol is strong, the engine may be flooded: wait a few minutes, choke off, then try again as the manual describes.
• For electric start: correct battery voltage, battery isolator on, terminals clean and tight.
• With the kill switch removed, take out the spark plugs with the right socket and look at them: wet, black, covered in deposits? If you have new plugs of the right reference, try them.
• Look at the visible fuel filter: water, deposits, dirty bowl. Petrol that is several months old is replaced with fresh fuel.

5. When to stop and call a professional

Call a mechanic if the engine still will not start with fresh fuel, a fuel supply that arrives, healthy plugs and a charged battery; if the pull cord or the engine are locked; if you keep finding water in the fuel; if the carburettor has to be taken apart; or if the engine starts but no water comes out of its cooling tell-tale (see no water from the exhaust). An engine that has been submerged or has taken in water must be seen very quickly, before corrosion sets in. Describe what you noticed: noise or silence, cold or warm, since the lay-up or in mid-season, and what you have already checked.

6. Keeping it from happening again

Buy your petrol in small quantities and use it within the season; before a long break, follow the manual (stabiliser, draining the carburettor float bowl or running the engine until it stops, depending on the model). Keep the tank sheltered, with the vent closed only for transport. Change the plugs and the fuel filter at the intervals in the manual, flush the engine with fresh water after trips at sea, and check the propeller and the primer bulb before the season. These steps belong in the winter lay-up and recommissioning list, and if you are thinking of changing engines, see how to choose an outboard.

In the Hullteam logbook, record every outboard service, the plugs, the filters, the water pump and repairs, with the date and the engine hours: an outboard whose maintenance can be proven sells better, with or without the boat (see which proofs count).