Why does my outboard crank but not start?

Cranks but won't start · Symptom: Engine turns over normally but never catches.

Quick answer: Most often: fuel not reaching engine: tank vent closed, empty tank, line not connected, primer bulb not pumped, clogged fuel filter / tank filter, stale or contaminated fuel. Start here: Open tank vent; confirm fuel level; reconnect hose fittings at both ends. If that doesn't fix it, work through the checks below, and see a marine mechanic if you're unsure.

Likely causes (most to least common)

Fuel not reaching engine: tank vent closed, empty tank, line not connected, primer bulb not pumped
Clogged fuel filter / tank filter
Stale or contaminated fuel
Wrong choke/enrichment use (flooded or not enriched)
Fouled/wet spark plugs or bad gap
Ignition fault (coil, sensor, ECU) or kill-switch wiring

Safe owner checks & fixes

Open tank vent; confirm fuel level; reconnect hose fittings at both ends.
Squeeze primer bulb until firm (see 15-primer-bulb).
Check/replace fuel filter per manual.
Check fuel in a clear jar for water/separation (see 10).
Pull plugs: wet = flooded (crank with throttle per manual's flooded procedure); dry = fuel delivery problem.
Inspect/replace plugs with manual-specified type and gap.

Parts / tools

Plug socket, spare plugs (type per manual), spare fuel filter, clear jar, fresh fuel.

Call a marine mechanic when

Fuel and plugs are confirmed good but no spark; you smell raw fuel in the cowl; EFI warning codes; low compression suspected after overheating. If you're on the water and unsafe, call TowBoatUS/Sea Tow or the Coast Guard (VHF 16).

Sources

Values not stated here are model-specific; check your owner's manual.