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Q&A: Outboard Trouble

Q: My outboard starts OK, but after a short time running it begins faltering and stops. And the bulb becomes flat. What’s the problem?

Q&A - Outboard Trouble

Q: My outboard starts OK, but after a short time running it begins faltering and stops. And the bulb becomes flat. What’s the problem?

A: There could be several causes. A likely theory would be that it’s getting starved for fuel. If your priming bulb is flat, this probably means there’s an obstruction between that and the tank. The motor is sucking fuel and eventually creates a vacuum in the line between the obstruction and the engine. The vacuum causes the bulb to go flat.

Numerous things could cause the blockage. Obviously, a first place to look would be your fuel filter — particularly if it’s between the bulb and the tank. Take a look at the element. If it appears to be dirty, replace it and see what happens. (It may be time to replace it anyway.) If the element appears to be unusually dirty, with deposits of gummy-looking material, you may need to have your tank professionally cleaned and your fuel line replaced. If it’s an external portable tank you can probably clean it yourself if you’re familiar with all the potential problems, techniques and safety precautions. Failure to do this correctly (or anything else with gasoline) could lead to explosion and death or serious bodily injury.

If you have a fiberglass tank, particularly an old one, and you’ve been using gas that contains ethanol, your tank could be degrading and/or gunk from the tank itself could be clogging your line or filter. Even if it’s a newer tank or the tank is made of another material, the ethanol fuel could be causing problems in the tank or with the fuel line, particularly if the line is old.

There are many reports as to the effects of ethanol gas on tanks, fuel systems and engines. A thorough discussion of this problem is beyond the scope of this Q&A, but Soundings has published several articles on the topic. (Search the story archives at Keyword: ethanol.) And BoatU.S. has information on the subject at its Web site ( Click on “Resource and Reference” on the menu bar at the top of the page, then on “Seaworthy magazine” from the drop-down menu. All boaters should carefully follow the ethanol issue, because it could have substantial effects relevant not only to performance but also to safety.

If your fuel filter is clean, you probably have blockage in the line. If your boat has a typical 6-gallon external tank, you might have an O-ring problem. Usually, the connecting coupling — the piece with the clamp that connects the fuel line to the tank fitting — has an O-ring up inside the hole through which the fuel flows. Its purpose is to seal the connection. If someone has tried to put on the coupling incorrectly, as is often the case when you have to quickly switch tanks when one unexpectedly becomes empty, sometimes the O-ring becomes damaged and/or distorted. The normal result of this is an air and/or fuel leak around the coupling, resulting in the engine being starved for gas, but probably not a flattened bulb pump. However, if the damaged or distorted O-ring blocks the fuel flow (possible but unlikely), it could cause the bulb to flatten.

Sometimes the hose will appear to be unobstructed, but the interior lining may have separated. Suction causes that inner lining to block the passageway. You probably can’t see this because the bulging out of the inner lining won’t occur except with use, and you, of course, can’t see up inside the line except at the end. If you have an old fuel line and/or a line not approved for this use, replace it.

It’s possible but unlikely that the bulb itself is causing the problem. They have what are essentially simple flap valves, each opening downstream of the flow.

Many fuel tanks, including external portable tanks, have a filter screen at the end of the pickup tube. Trash or gunk on this may be the culprit. With a portable tank you can often visually inspect the screen, but remember that gas fumes can cause serious injuries, including to your eyes. And use of a flashlight to see inside this type or any type of gas tank, unless the light is completely airtight and ignition-proof, could cause an explosion.

Gasoline-related problems on boats are inherently dangerous. If they aren’t handled correctly and with safe methodology, death and/or serious bodily injury could occur in the process of diagnosing and making the repair or during use of the boat. It’s best to get a well-qualified professional who’s fully trained and experienced in all of the safety precautions and proper methodology, and who has proper equipment and skills if you need to do anything with the tank, the fuel line or with any other component or issue relating to your fuel system.

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