Outboard won't start?
Check the simple things first.

1 · Outboard cranks but won't start

This is the most common outboard problem there is, and it has two causes that take five seconds each and embarrass everyone once: the kill-switch lanyard and the tank vent. After those, it's the same story as every small engine that sat — gasoline starts going stale in as little as 30–60 days, and by the first launch the carburetor's tiny jets are varnished shut. The engine is mechanically fine and simply can't drink, or can't spark.

Work the causes in this order. Each one is cheaper and more likely than the next, and most owners are on the water by step 3.

The fix, step by step

1. Clip the lanyard and confirm neutral. Push the kill-switch clip fully onto the switch — an outboard will crank all day with zero spark if it isn't seated, because that's exactly what it's designed to do when a driver goes overboard. Most motors also refuse to start in gear: shift to neutral and wiggle the handle to be sure.

   

2. Open the tank vent. On a portable tank, unscrew the vent on the cap a turn or two. As the motor drinks, air has to get in; a closed vent starves it as surely as an empty tank. On a built-in tank, check the vent hose isn't kinked or blocked by a wasp nest after storage — it happens every spring.

   

3. Squeeze the primer bulb until it's firm. Arrow on the bulb pointing toward the motor. Firm bulb = fuel at the carb. Bulb that never firms up = air getting in where fuel should be: push both quick-connectors on until they click, check the bulb itself and the line for cracks (ethanol fuel hardens them from the inside), and confirm the tank pickup isn't clogged.

   

4. Drain the old fuel completely. If the gas sat all off-season, don't try to “burn through it.” Drain the tank and the carburetor bowl/float chamber into an approved container and refill with fuel bought this season, plus stabilizer. Dispose of stale fuel per your local rules — never on the ground or in the water.

   

5. Clear a flood before you chase anything else. Too many primes or too much choke drowns the plug. Choke fully OFF, throttle open, crank 8–10 times. Still nothing? Pull the plug, dry it, crank a few times with the plug out to clear the cylinder, and retry with no choke and no prime.
6. Pull the spark plug(s) and read them. Black and sooty = rich/fouled. Wet with fuel = flooded or no spark. White or blistered = overheating (see section 4). Fouled plugs are cheaper than the time to clean them: replace with the exact plug and gap in your manual, and confirm spark with an inline tester — don't hold a bare plug by hand.

   

7. If it fires on a bulb-prime but won't stay lit, it's the carburetor. Remove the bowl, clean the main and idle jets and passages with carb cleaner and a single strand of copper wire — never a drill bit or steel wire, which enlarge the holes — and reassemble. A rebuild kit (gaskets, needle, seat) is the reliable fix when cleaning alone doesn't hold.

   

   

2 · Starts, then dies

A motor that starts proves it has fuel, spark, and compression — at least for a moment. Dying is about what runs out. When and how it dies tells you what:

Dies on a timer — runs 1–3 minutes, quits, restarts after sitting

The tank-vent vacuum lock, and outboards hide it better than any other engine. As fuel drains, air must enter through the vent; if the vent screw is closed or the vent is clogged, a vacuum builds until it beats the fuel flow and the motor starves. Sitting lets air slowly leak back in, so it restarts like nothing happened. Open the vent fully; on a portable tank, try running briefly with the cap loosened — if the dying stops, you've confirmed it.

Dies unless you keep squeezing the primer bulb

You're doing the fuel pump's job by hand. The engine's fuel pump is weak or its diaphragm is tired, or the pickup inside the tank is clogging. Check the vent is fully open and the pickup screen is clear first (both free), then test or replace the pump.

Dies the moment you shift into gear or throttle up

It idles on what's in the bowl but can't make power: a partially blocked main jet, a clogged inline fuel filter, or a collapsing fuel line. Enough fuel to idle, not enough to work. This is a carburetor cleaning and a $5 filter (section 1, step 7), not an adjustment to live with.

Dies hot, restarts fine once it cools

A cracked spark plug or a failing ignition coil can spark cold and quit as it heats up — the motor dies like someone flipped a switch. New plug first (cheap, ten minutes); if it still dies hot, test for spark with an inline tester immediately after it dies. No spark while hot = coil.

3 · Runs rough, shakes, or won't idle

Idling is the hardest thing an outboard does all day: it takes the least fuel, at the lowest speed, and shifting into gear adds load at exactly that weakest point. That's why rough running almost always shows up at the dock first.

Stalls when you shift into gear is the signature of a partially clogged idle jet or water in the fuel — a bead of water sits in the bottom of the bowl and won't burn. Drain the bowl and the water-separating filter (where fitted) into a clear container and look at it: cloudy fuel, separated layers, or rust flecks mean drain the tank too.

Surging — revs rising and falling in a steady hunting rhythm at a fixed throttle — is a mixture swinging rich and lean: a half-blocked jet, or extra air sneaking in past a cracked intake gasket, perished fuel line, or loose carburetor. Squeeze rubber lines; cracks open up. Check carb mounting bolts for tightness.

Blubbering, smoking, and loading up at idle (2-stroke) often traces to the fuel itself: the wrong oil mix. Too much oil fouls plugs and carbon-loads the motor; too little oil is an engine-killer, not a tuning choice. Mix exactly to the ratio in your manual, in a clean can, with fresh fuel — and when in doubt about a can's ratio, dump it and mix a known batch.

Adjustment comes last, not first. On older outboards with adjustable jets, set the idle mixture per your manual, in gear, in the water or on muffs — never by ear alone at high RPM out of water, and never rev a motor on muffs beyond a fast idle: there's no load and no proper cooling margin. If the adjustment keeps drifting, the carb needs cleaning or a kit; a screw can't compensate for a clogged jet.

4 · No tell-tale stream, steam, or overheating

The tell-tale — the small stream of water from the side of the motor — is your cooling system's heartbeat. A strong stream should appear within seconds of starting. Weak stream, no stream, or white “smoke” that is really steam means cooling water isn't circulating. Stop the motor. An overheated outboard can be destroyed in minutes, and every minute of “running it to see” is scored cylinder walls.

Check the simple blockages first

Kill the motor and look at the intake screens on the lower unit: weeds, a plastic bag, sand, or barnacles (on a slipped boat) block them constantly. Clear them and retry. Also check the tell-tale outlet itself — mud daubers and debris plug the little nozzle over storage, and a thin wire or a blast of air clears it. Strong water at the intakes + a plugged outlet reads exactly like a dead pump, and it's a two-minute fix.

Then suspect the impeller

If intakes and outlet are clear and the stream is still weak, the water pump impeller is worn out. It's a flexible rubber wear part that lives in the lower unit, and it's meant to be replaced every couple of seasons. It fails in two classic ways: vanes that take a set and crack after long storage (the spring no-start that also doesn't pee), and vanes shredded by running in sand or — fastest of all — running the motor dry without water for even a few seconds. Replacement means dropping the lower unit and fitting an impeller or full pump kit with fresh gaskets: a doable driveway job with the manual for your model, basic hand tools, and gear oil to refill what drains. Note the shift-shaft alignment on reassembly — that's the step that makes it a shop job when rushed.

Still overheating with a new impeller?

Next suspects are a stuck thermostat (it never opens, so the powerhead overheats even with water flowing) and, on older motors, salt and scale narrowing the cooling passages. Both are diagnosable, but this is the honest point to get a shop involved if the basics are done.

5 · Lacks power — won't get on plane, bogs at speed

A motor that runs but can't do its work is rarely one problem — work from the back of the boat forward, because the cheapest causes are behind you.

Prop first: bent blade or spun hub

A dinged or bent blade wastes serious power and vibrates doing it. A spun hub — the rubber hub inside the prop slipping under load — is sneakier: the motor revs, the boat barely moves, exactly like a slipping clutch. Test it: draw a line across the hub and the prop shaft end, run the boat under load, and check whether the marks have separated. Separated marks = the hub is slipping; the fix is a rehub or a replacement prop, and carrying a spare prop (with a spare nut and cotter pin) ends the trip-ruiner version of this problem.

Then the hull and the load

A hull fouled with algae and growth can eat a third of your speed — the motor gets blamed for the boat's drag. Scrub it before you tune anything. Then check the obvious: weight distribution (everyone and the cooler in the stern will keep any boat from planing), motor trim angle, and whether the motor is mounted at the right height — a motor buried too deep drags its lower unit like an anchor.

Then the engine under load

If the prop and hull are honest, a partially blocked main jet starves the motor exactly when it works hardest — it will idle and troll all day and bog the moment you ask for power. The tell: partial choke restores power. That confirms fuel delivery, full stop: clean the carb, replace the inline filter, and check for a collapsing fuel line or weak fuel pump (section 2). On a 4-stroke, also check the air intake for a storage nest — it happens more than anyone admits.

6 · Prevent it: winterizing & spring checklists

Almost every repair above traces back to one autumn afternoon that didn't happen. Outboards live stored longer than almost any other engine — a little care at layup deletes most of this guide.

End of season (the hour that matters)

• Add fuel stabilizer and run the motor on muffs long enough for treated fuel to reach the carburetor — or drain the system dry, per your manual's storage method. Pick one; doing neither is the problem.
• Fog the cylinders (or follow your manual's storage-oil procedure) and change the engine oil on a 4-stroke while it's warm from that run.
• Change the lower-unit gear oil now, not in spring — and read the old oil. Milky oil means water is getting in, and it's far better to learn that in October than at the launch.
• Grease the fittings, pull the prop, grease the shaft, and check for fishing line wrapped behind the prop — line eats the seal it hides behind.
• Charge the battery, disconnect it, and store it somewhere it won't freeze flat. Clip the lanyard around the tiller or control so spring-you finds it.
• Note the impeller's age. Every couple of seasons is the replacement rhythm — a spring failure is a choice made by skipping this line two years running.

First trip (in the driveway, before the launch)

• Run the motor on muffs at home. A no-start in the driveway is an errand; at a busy launch with a line behind you, it's a story.
• Watch the tell-tale for a full minute. Strong stream before you go = a trip that starts with confidence.
• Buy fresh fuel for the season — don't start spring on last fall's gas can, stabilized or not.
• Squeeze the primer bulb and check every fuel line and connector for cracks, softness, and clicks.
• Confirm the spare prop, plug, and lanyard clip are in the boat — the three spares that have saved the most trips.

Related troubleshooting guides

General repair guidance for common small outboards — always check your owner's manual for model-specific specs, fuel/oil ratios, torque values, and part numbers.