Engine Starts Then Dies - Troubleshooting Guide

A loose lanyard clip or a worn switch can cut the engine as you move. Make sure the clip is fully seated. If it dies when you bump the helm, the switch or its wiring may be faulty.

A closed or blocked fuel tank vent creates a vacuum and the engine starves after a few minutes. Open the vent on a portable tank. On a built-in tank, a blocked vent (insect nest, kinked hose) often shows as a "whoosh" of air when you open the fuel cap. If loosening the cap lets the engine run, fix the vent.

On outboards, if squeezing the primer bulb keeps the engine alive, it is not getting enough fuel on its own. Look for a collapsed bulb, a bad bulb check valve, a kinked line, a loose quick-connect fitting, or a torn O-ring letting air in. Check that the arrow on the bulb points toward the engine. BoatUS notes that a bulb gone hard and stiff has tired one-way valves inside and can shed rubber into the fuel, so replace it instead of nursing it along.

Make sure there is enough fuel, the tank selector or fuel valve is fully open, and the line is not kinked by gear or a hatch. A low tank in rough water can uncover the pickup.

Look in the filter bowl or remove the filter and pour some fuel into a clear container. Water or debris means contaminated fuel. Replace the filter. Ethanol fuel can loosen deposits in old tanks and clog filters quickly; carry a spare.

An engine that dies suddenly and completely, with no sputtering, often has water in the fuel. If the filter is full of water, the tank needs to be pumped out and cleaned. Additives will not fix water-contaminated or phase-separated fuel. Do not keep restarting: you can draw more water into the engine.

Even if the water-and-ethanol layer at the bottom never reaches the pickup, Mercury explains that the gasoline left on top has lost much of its ethanol and can drop by up to about 3 octane numbers, which can cause rough running or engine damage. Phase-separated fuel has to be removed, the tank cleaned and refilled with fresh fuel.

Fuel that sat for months untreated can go stale and gum up the idle circuits of carburetors and injectors. Test with a portable tank of fresh fuel connected directly to the engine. If it runs fine on fresh fuel, the problem is in your main tank's fuel.

Many boats with built-in tanks have an anti-siphon valve at the tank outlet. If it sticks, it restricts fuel flow, especially at higher demand. If the engine runs on a portable tank but not on the built-in tank, have this valve and the pickup checked.

If it only dies when shifting into gear:

• Check the idle rpm against your manual; it may be set too low or dropping when the engine is cold.
• Check the prop for rope, line or weeds (engine off, key removed).
• Have a dealer check shift cable adjustment if shifting is stiff or harsh.

Many modern engines shut down or limit power when they overheat or oil pressure is low. Look for warning icons, check the telltale or exhaust water, and check the oil level. See the overheating guide if water flow is weak.

A weak battery or loose connection can make modern fuel-injected engines stall, because the fuel pump and computer need steady voltage. Clean and tighten battery and engine ground connections. Measure the voltage with the engine running; it should be higher than with the engine off if the charging system is working.

On carbureted engines, a choke that stays on, or one that is not used on a cold engine, can make it die. After storage, check for nests or debris in the air intake.

If the fuel supply checks out and it still stalls, the cause may be a failing fuel pump, clogged injectors or carburetor, a vapor separator problem, or a bad sensor. These need a dealer's diagnostic tools and fault code reader.