Sort the complaint first

"Won't start" means three different jobs: no crank, cranks but no fire, or fires and dies. Get the customer to describe it (or video it) before you load the truck — it changes what you bring.

No crank

1. Lanyard/DESS-style security: confirm the correct transmitter/clip is present and the ski isn't in a locked/security mode. On Yamahas with a lanyard, verify it's seated — the number of "dead ski" calls solved by a mis-clipped lanyard is humbling.
2. Battery: load-test, not just volts. PWC batteries are small and die young; corroded terminals under the seat are routine.
3. Starter relay (solenoid): click but no crank = jump the relay posts carefully to isolate relay vs starter. No click = start switch, wiring, or safety interlock.
4. Starter itself: PWC starters live wet lives; a dead starter with a rusty case tells you water is getting into the engine bay — find out how.
5. If the engine won't turn by hand (plugs out, socket on the crank per the manual): suspect hydrolock or seizure — stop cranking immediately.

Cranks, no fire

1. Pull a plug, ground it properly, check spark with an inline tester.
2. No spark: check kill circuit/lanyard switch first, then fuses, then stator/pickup per the service manual values.
3. Spark present: fuel — listen for the fuel pump prime (EFI models), check fuel pressure at the rail against the manual's spec, inspect for stale/varnished fuel from storage.
4. Compression test if spark and fuel check out — a season of hard use or a lean two-stroke history shows up here.

Fires and dies

Classic stale-fuel/idle-circuit behavior on older carbureted models; on EFI think fuel pressure bleed-down, a failing fuel pump, or a clogged in-tank filter sock.

Common mistakes

• Cranking endlessly on a hydrolocked engine (bends rods — pull plugs first if there's any chance of water ingestion)
• Replacing the starter when the real fault is a corroded ground under the seat
• Ignoring why the electrics corroded — hull leak, missing seals, or a habitual submariner owner

When to walk away

No hand-rotation plus rusty water at the plug holes = internal corrosion lock. Quote a teardown/recovery honestly rather than a magic dockside fix.

Safety: fuel vapor collects in PWC hulls — open the seat and ventilate before working; disconnect the battery before starter work.