The starter spins the engine over strong, but it just won't catch. Here's the logic that saves you money: if it's cranking, your battery and starter work — so the engine is only missing one of three things: spark, fuel, or the OK from the ignition/security system. The trap most people fall into is buying an expensive part when the real problem is a corroded connector or a tank of bad gas. Below: the shared checks first, then the fixes split by engine — skip straight to your type.

Start with these — any Sea-Doo

1. Charge or load-test the battery. A battery strong enough to crank can still be too weak to fire the coils or run the fuel pump — you'll sometimes get a click instead of a crank. Charge it fully and clean/tighten both terminals and the ground strap.
2. Do the spark-vs-fuel test. Pull a plug and check for spark: ground the plug threads against bare metal, crank, and look for a fat blue spark. No spark or weak yellow spark = work the ignition side. Good spark = work the fuel side. This one move tells you which half of the ski you're fighting.

Read the plug you just pulled (works on any Sea-Doo)

That plug is a free diagnostic gauge — the tip tells you what's going on in the cylinder:

Check the gap against your spec while it's out, and honestly — plugs are cheap. If they're fouled, worn, or you're not sure how old they are, just put in fresh plugs as your first move. A fouled plug alone will keep a ski from starting.

Check the fuel — pull a sample (any Sea-Doo)

Old or watered fuel is one of the most common no-starts, and it hides. Don't guess — pull a sample and look at it:

1. Relieve fuel pressure (4-TEC) or shut the fuel valve (2-stroke), then crack the line at the fuel filter or pump inlet and catch a few ounces in a clear glass jar. (You can also siphon from the bottom of the tank, where water settles.)
2. What good fuel looks like: bright, clear, one uniform color, and it smells like gasoline.
3. Water in the fuel: a separate clear layer sitting at the bottom of the jar, or a cloudy/milky look. This is ethanol phase separation — the water won't burn and it sits right where the pickup draws from. Extremely common in a ski that sat.
4. Stale fuel: dark amber/brown color and a sour, varnish, or turpentine smell instead of gas.
5. Debris: rust flakes or sediment = a dirty tank or rotting lines.

If the sample is bad: drain the tank completely, replace the fuel filter, and refill with fresh fuel and stabilizer. Then check your fuel cap seal and tank vent — that's usually how the water got in.

4-Stroke Sea-Doo (4-TEC, fuel-injected — 2002 and newer)

First free check on any 4-TEC: clean the DESS post & key. Green or white crust on those pins is one of the most common no-starts there is, because the ski won't authorize. Clean the post and the underside of the key with a pencil eraser or contact cleaner, reseat, and retry. Still dead? Try a known-good key.

4-TEC — no spark

Two things to know before you spend money. First, a 'dead MPEM' is very often just corroded connectors — the module sits in a bad spot and its plugs corrode, especially in salt water. Unplug, clean the pins, add dielectric grease, and retest first. Second, to test an ignition coil: swap the suspect coil onto a known-good cylinder — if the dead spark follows the coil, the coil is bad; if it stays put, it's the plug or wiring. You can also ohm the coil's primary and secondary windings against spec.

4-TEC — has spark, no fuel

The money-saver most people miss: if you attach the key and don't hear the fuel pump buzz for ~2 seconds, don't assume the pump is dead. On 4-TEC skis the fuel pump gets its ground through the ECM's 40-pin connector — when that connector corrodes, the pump never primes. Unplug the 40-pin ECM connector, clean it with contact cleaner (DeoxIT), reseat it, and a huge share of 'dead pump' skis prime right up and start. Do that before buying a pump.

On the injectors: a clogged injector makes a cylinder run lean, misfire, and hard-start; a leaky injector floods its cylinder and makes fuel pressure bleed down after the pump shuts off (hard hot-starts, black plug on that hole). A leak-down test tells them apart: pressure should hold near 58–60 PSI for a few minutes — a fast drop points to a leaky injector, a bad regulator, or a pump check valve. Injectors can sometimes be professionally ultrasonic-cleaned and flow-tested, but if they're leaking or won't clean up, replace them.

2-Stroke Sea-Doo (carbureted — older skis)

First free check: make sure the tether/lanyard cap is fully seated on the stop switch. Then work spark or fuel based on your plug test.

2-stroke — no spark

Same rule as the 4-TEC: most 'dead MPEM' 2-strokes are actually corroded connectors, and the MPEM sits in a spot that loves to corrode in salt water. Clean the pins and add dielectric grease before you spend a dime — confirm a genuinely bad MPEM by swapping it into a known-good ski. Also check the plug caps: they thread onto the wire and their resistance drifts or the wire corrodes, killing spark. Unscrew, trim back fresh wire, and reinstall.

2-stroke — has spark, no fuel

Know this trap if your ski is pre-2001: the factory gray Tempo fuel lines rot from the inside out. The crumbs travel downstream and plug the tiny internal filter inside the Mikuni carburetor. The tell-tale sign is a ski that starts and idles on the trailer but bogs down under load — and eventually won't start at all. A carb kit alone won't fix it if the lines are still shedding debris.

The proper fix, in order:

1. Replace ALL the fuel lines with ethanol-rated line (don't reuse the gray stuff). Keep supply and return straight — don't swap them.
2. Clean or replace the fuel selector valve (the ON/OFF/RESERVE knob) — they clog and can draw air.
3. Rebuild the carburetors, including the small internal filter screens, with a fresh kit.

One more 2-stroke gotcha: every fuel joint has to seal. A cracked line, a loose clamp, or a leaking crankshaft seal lets the engine draw air, run lean, and become a miserable hard-starter. If it starts but won't idle after a rebuild, pressure-test the crank seals.

Both spark and fuel, and it STILL won't run? (either engine)

• Flooded. Plugs soaked. Hold the throttle wide open (adds no fuel) and crank to clear it, or dry/replace the plugs.
• Low compression. A high-hours 2-stroke with worn rings or a scored cylinder will crank fast but never fire. Run a compression test before chasing fuel and spark in circles — this is the check that ends the guesswork.
• Water in a cylinder (hydrolock). A bad flush or a tip-over pushes water into a cylinder. Pull the plugs and crank to blow it out before it fires — running it wet bends rods.
• A code is stored (4-TEC). If your gauge is throwing a P-code, look it up first — see our Sea-Doo fault code guide.

The short version

Pull a plug — it tells you spark-or-fuel and shows you rich, lean, or oil-fouled in one look. Pull a fuel sample and check for water. 4-TEC: clean the DESS post, then clean the ECM connector before buying a pump; swap-test coils; leak-test for a bad injector. 2-stroke: on an older ski, assume the gray fuel lines and rebuild the fuel system as a set; clean connectors before condemning an MPEM. Ninety percent of no-starts are hiding in that list.

Get the parts for your ski

Match to your exact year and model on the collection pages:

Always work cheapest-to-most-expensive: read the plug, check the fuel, and clean connections before you buy a pump, injectors, or a module.