Jet ski won't start?
Check the simple things first.

1 · Jet ski won't start

This is the most common PWC problem there is, and on a modern ski it's electrical more often than mechanical. Three separate systems can veto a start before the engine ever gets a vote: the safety lanyard, the security key, and the battery — and a battery can pass the "it cranks, doesn't it?" test while still being too weak for the ECU and starter solenoid to do their jobs. Only after those three come fuel and spark, the same story as every engine that sat: gasoline goes stale in 30–60 days.

Note what your ski does when you hit start, because it splits the list in half: nothing at all (no crank, maybe a single click) points at the lanyard, key, battery, and solenoid; cranks but won't fire points at spark and fuel. Work the causes in this order — each is cheaper and more likely than the next.

The fix, step by step

1. Seat the lanyard like you mean it. Push the clip fully onto the kill-switch post until it sits flat — a half-seated lanyard is the single most common "dead ski" there is. On many models a missing lanyard means no spark; on others, no crank at all. Clip it to yourself for the test, not to the handlebars.

   

2. Listen to the key. Put the security key on its post and pay attention. On a Sea-Doo, two short beeps means the DESS system read the key and you're cleared to start. A long beep, four beeps, or silence with a key warning means it didn't: wipe the post and the inside of the key cap clean and dry, try the spare key, and make sure it's the key programmed for this ski — keys from a second ski (and the restricted learning key) won't clear it. Yamaha and Kawasaki use their own security fobs and lock modes — check the dash isn't showing a locked state.

   

3. Charge the battery, then load-test it. Don't trust "it cranks." PWC electronics are voltage-sensitive: a battery can spin the starter and still sag so low under load that the ECU and solenoid drop out mid-crank. Charge it fully, scrub the terminals shiny, tighten the cables so they can't twist by hand, and load-test — a battery that can't hold voltage under load is done, however new it looks. A battery that sat discharged all winter is usually sulfated and won't come back.

   

   

4. One click = solenoid territory. With a tested-strong battery and clean terminals, a single solid click and no crank points at the starter solenoid — a cheap, bolt-on part on most skis. A whirring starter that doesn't turn the engine over is the starter drive not engaging; that's usually a starter replacement, and on many models it's buried enough to be a shop job.
5. Satisfy the interlocks. Some models won't crank unless they're in neutral or the brake/reverse lever is in the right position. Check your manual, set it, and try again before you take anything apart.
6. Clear a flood before chasing fuel parts. Strong fuel smell after a lot of cranking? The engine is drowned, not starved. Follow the clear-flood procedure in your manual — on many fuel-injected skis, holding the throttle wide open while cranking tells the system to cut fuel and just pump air — then retry normally.
7. Drain stale fuel and refill fresh. If the ski sat all off-season, don't try to "burn through" the old gas. Drain the tank 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.
8. Pull the plugs and read them. Black and sooty = fouled. Wet with fuel = flooded or no spark. On a two-stroke, plugs foul fast and are a consumable, not a diagnosis. Replace with the exact plug and gap in the manual and confirm a strong blue spark with an inline tester — don't hold a bare plug in your hand while someone cranks.

   

9. Still dry with good spark? Fuel delivery is last. Check the fuel filter for clogging and listen for the fuel pump priming when the key goes on (fuel-injected models). A silent pump with good fuses, or a filter full of debris and water, has found your problem.

2 · Starts, then dies

A ski that starts has fuel, spark, and compression — something runs out, gets interrupted, or gets shut down. The pattern is the diagnosis: when it dies tells you which system to open first. Read the pattern that matches yours before touching parts.

Dies immediately — the kill switch is doing it

If the ski dies the moment you shift your weight, turn the bars, or the hull rocks, suspect the lanyard clip itself. The clip and the post wear, and a worn clip sits loose enough that vibration pops it off the switch — which cuts the engine exactly as designed. Swap in a known-good lanyard (this is why you carry a spare) before diagnosing anything else.

Dies after a few seconds — it's starving

1. Restart test. If it restarts after sitting a minute and dies again on the same schedule, fuel is arriving slower than the engine drinks it: it runs on what seeps through, empties the line, and quits.
2. Replace the fuel filter. Cheap, and the most likely restriction — especially after a winter on stale fuel.
3. Trace the fuel line for pinches and kinks, particularly where the seat or storage bin closes over it, and confirm the tank vent isn't blocked — a vent that can't breathe starves the ski the same way (see the vent pattern in the outboard guide — same physics, smaller tank).
4. Check the fuel itself. Siphon a sample into a clear jar: water settles to the bottom, and stale fuel smells like varnish. Either way, drain and refill fresh.

Dies when warm — heat is the trigger

Runs clean from cold, quits once it's fully hot, restarts after a cool-down: that's a heat-soak fault. On the simple end, check that the cooling system is actually flowing (a half-blocked cooling line makes everything under the seat hotter than it should be — go to section 5) and that plug caps are seated and dry. On the deeper end, ignition components and sensors that fail only when hot need a shop's diagnostic time — flag it honestly and don't shotgun parts at it.

Dies in rough water — something's loose or wet

1. Wiggle-test the battery cables at the dock with the engine idling on the trailer (briefly, per the safety box). If a wiggle kills it, clean and properly tighten the terminals — hand-snug isn't enough on a ski that pounds over wakes.

   

2. Open the seat and look for water. A bilge that keeps filling points at a leak, a failed drain, or water left over from a capsize. Sloshing water reaches plug caps and electrical connectors in chop that it never touches on flat water.
3. Dry and seat the plug caps. Pull each cap, dry it, and push it back on until it clicks or seats firmly. Cracked caps that arc when wet are a cheap replacement.

3 · Runs rough, shakes, or won't idle clean

Rough running is the engine telling you the mixture or the spark is almost right. On a ski, the causes are refreshingly unglamorous: plugs, old fuel, and water — in that order — account for most of it. Two-strokes add one more: they foul plugs and load up with carbon as a way of life, so "rough" on a two-stroke starts at the plugs every time.

The fix, step by step

1. New plugs first — correctly gapped. Pull each plug, read it (black = rich/fouled, wet = flooding or water, white = lean/hot), and replace rather than clean. Confirm the gap against the manual: a plug that's "close" out of the box can still be wrong for your engine, and a two-stroke will find that gap.

   

2. Sample the fuel. Siphon a cup into a clear jar and let it settle. A distinct water layer at the bottom, or fuel that smells sour instead of sharp, ends the diagnosis: drain the tank completely, replace the filter, refill fresh.

   

3. Feed it fresh fuel and run it. Half of "rough running" cures itself within minutes on good gas once the old blend is fully out of the lines. Judge it after a real run, not at idle on the trailer.
4. Check the two-stroke oil — the right oil, actually present. Confirm the oil tank has the spec of oil your manual calls for (two-stroke oils are not interchangeable across brands and types), and that the level is genuinely dropping in use. No smoke at all on a two-stroke that should have some is a warning, not good news — and many models drop into limp mode when the oil tank runs dry (see section 4).
5. Then suspect injectors or carb jets. If plugs and fuel are new and it still stumbles, fuel delivery is partially blocked — varnish in a carb jet or a clogged injector. Run a quality fuel-system cleaner through a fresh tank first; a carb comes apart for cleaning if that fails.
6. Look for leaks last. A surging, hunting idle that won't settle often means unmetered air: check intake boots and hoses for cracks and loose clamps, and exhaust connections for leaks under the seat.

4 · Revs climb, but it barely moves — cavitation & lost thrust

This is the signature PWC problem, and it fools people because the engine sounds healthy — revs climb happily while the ski wallows. A jet ski has no propeller and no gears: the engine spins an impeller inside a pump, and thrust is just water in through the intake grate under the hull and out the nozzle. Anything that breaks that clean flow of water — blockage in, leakage inside, damage to the impeller — gives you noise instead of push. Mechanics call the result cavitation: the impeller spinning in frothed, aerated water instead of a solid stream. Diagnose the pump before you touch the engine; the engine is usually innocent.

The fix, step by step

1. Engine OFF, lanyard in your pocket. Everything in this section happens with the engine fully off and the lanyard pulled — hands go near the intake grate and driveshaft, and a bumped start button with your fingers in the pump is how people lose them.
2. Clear the intake grate. Get the ski out of the water, or reach under the hull from behind/below as your manual directs. Weeds, a plastic bag, a chunk of wood, or a rock jammed in the grate strangles the pump. Pull everything out and check again by feel — debris hides ahead of the impeller.

   

3. Check the driveshaft for a rope. The classic: the ski tows a tube, the slack rope drifts under the hull at idle, and the pump inhales it. Rope wraps tight around the driveshaft ahead of the impeller. Unwind it or cut it away strand by strand, and look for rope melted into the shaft seals — damaged seals make this a shop job (see the FAQ).

   

   

4. Inspect the impeller. Shine a light up through the grate and in from the nozzle. Leading edges should be smooth and sharp-ish, not nicked, bent, or chewed. Gravel through the pump dings edges fast, and every nick bleeds thrust. Small nicks can be filed smooth; bent blades are a replacement.

   

   

5. Check the wear-ring clearance. The impeller spins inside a replaceable wear ring with a gap of only a few thousandths of an inch. As the ring wears (sand is an abrasive, and it goes through the pump all day), the gap grows and pressure leaks around the impeller instead of pushing out the back — the ski still revs, it just slips. Measure the impeller-to-ring clearance with a feeler gauge against your manual's spec where the design allows. Out of spec = new wear ring: it's a wear part, priced like one, and it's the single most satisfying fix in PWC ownership.

   

   

6. Rule out the computer. If revs are capped at a clean, consistent limit with a warning on the dash, the ski is protecting itself in limp mode — most often for overheating (go to section 5) or, on two-strokes, an empty oil tank. Top up the oil or fix the cooling first; the power comes back on its own.
7. And rule out a misfire under load. If thrust pulses or stumbles as the revs rise rather than slipping smoothly, swap in fresh plugs (see section 3) before you pull the pump apart — a plug that fires at idle can quit under load.

5 · Overheating — beeper, limp mode, or a weak pisser stream

Most PWCs are open-loop cooled: there's no radiator and no coolant — the jet pump draws lake water in and circulates it straight through the engine, then out. That design is simple and works brilliantly right up until the water stops flowing, at which point you have an engine being cooled by nothing. An overheat warning on a ski is not advisory. Stop, find the blockage, and only then ride — gently — back.

The fix, step by step

1. Stop at the first beep. A continuous warning beeper, a temperature light, or the ski dropping into limp mode (revs capped) is the engine asking for exactly one thing: off. Idling "just to get back" on a blocked intake cooks seals and warps heads. Get towed or drift and fix it.
2. Check the intake grate first. Engine off, lanyard out. The same weeds, bag, or shell that blocks thrust blocks cooling — on most skis they're the same mouthful of water. Clear it (per section 4) and half of all overheat warnings are already fixed.
3. Read the tell-tale. Where fitted, the pisser stream is your flow gauge: it should be a strong, steady stream at idle once warm. Weak or absent with a hot engine = water isn't circulating. Weak stream with a cool-running engine is often just the pisser outlet itself plugged with sand or salt — clear it with a small wire or compressed air before assuming worse.

   

4. Flush the cooling lines. Sand pumped in the shallows settles in cooling passages. On the flush port, back-flush the system following your manual — and get the order right: engine running first, then water on; water off first, then engine off. Water pressure into a stopped engine can push water where it should never go.

   

5. Make flushing a habit, not a repair. After every saltwater ride and every shallow, sandy day: a brief fresh-water flush on the hose, same on/off order, every time. Salt and sand buildup is the slow cause behind most "mystery" overheats on coastal skis. Some models are closed-loop (they carry coolant like a car, with lake water cooling only the ride plate/exhaust) — if yours is, check coolant level too and follow that manual's procedure.
6. Four-strokes: suspect the thermostat. Clear intake, strong stream, clean flush — and it still heats up? A thermostat stuck shut does exactly that. It's a cheap part; test or replace it before suspecting the sensor or the engine.

6 · Prevent it: winterizing & spring checklists

Almost everything in sections 1–5 is a storage injury: stale fuel, a sulfated battery, fouled plugs, sand left in cooling lines. One careful hour in the fall buys you a ski that starts on the first warm Saturday — and in Minnesota, that Saturday is not one you want to spend in the driveway with a multimeter.

End of season (the hour that matters)

• Stabilize the fuel, then run it in. Add fuel stabilizer to a full tank of fresh fuel and run the ski briefly (on the hose, correct order) so treated fuel reaches the whole system — or drain the system entirely if your manual prefers it.
• Fog the engine — critical on two-strokes. Fogging oil through the intake (and into the cylinders per your manual) coats internals against a winter of condensation. Four-strokes: follow the manual's cylinder-oiling procedure.
• Flush, then drain the cooling system. Final fresh-water flush, then drain residual water from the exhaust and cooling lines so nothing freezes and cracks. Short bursts of throttle (engine only, per the manual) help blow water out of the exhaust.
• Antifreeze where the manual calls for it. Some models want RV/marine antifreeze run through the cooling loop for winter; closed-loop models differ — they keep their own coolant and have a different procedure. This is the step to read your manual for, not to guess.
• Four-strokes: oil and filter now, so it sits all winter on clean oil instead of used, acidic oil.
• Battery out and on a tender. Remove it, store it somewhere that doesn't freeze hard, and keep it on a maintainer — not a dumb charger cooking it for five months. A battery left flat in the ski is next spring's section-1 problem.
• Clean, dry, and cover. Wash off salt and scum, dry the engine compartment, leave the seat cracked or off for airflow, and cover it. Check the intake grate and impeller one last time while you're down there.
• Trailer bearings. A ski that starts perfectly but loses a wheel bearing on the way to the lake still ruins the day — repack or at least inspect the bearings while the tools are out.

First ride (in the driveway, before the launch)

• Charge and load-test the battery before it goes back in; clean terminals, tight cables (section 1, step 3).
• Fresh fuel. If the tank sat on last fall's fuel without stabilizer, drain and refill — don't gamble the first ride on it.
• Inspect the pump before the first launch: intake grate clear, impeller edges clean, wear-ring clearance in spec (section 4). Winter is when this job is pleasant.
• Test the lanyard and kill switch for real: start it (briefly, on the hose, correct on/off order), pull the lanyard — the engine must die instantly.
• Flush-test on the hose briefly and watch the tell-tale stream — strong and steady before the ski ever touches the lake (section 5).
• Drain plugs IN. Say it out loud at the launch. Every spring, someone doesn't. Check the bilge is dry and the plugs are home before the hull leaves the trailer.

Related troubleshooting guides

General repair guidance for common personal watercraft — always check your owner's manual for model-specific specs, key programming, flush procedures, torque values, and part numbers.