Got a fuel problem? Troubleshoot it

Not all mechanical problems are the result of a failed engine. In a recent e-mail, a boat owner described a problem he was having with the brand-new engine he had just re-powered his boat with. He explained that he had performed the usual break-in, and liked what he had seen up to that point.On his next trip, everything went smoothly for the first half hour of operation; then all of a sudden, the engine started to sputter, and it died. He could not get it to restart. He began inspecting the fuel line, and discovered that the primer bulb was soft and had no pressure.

After pumping the bulb, he got the engine to start immediately, but it died again when he attempted to accelerate to a planing speed. Being cautious and not wanting to do any damage to his new engine, he got towed back to the dock, and the next day took his rig to the dealer to be checked.

After careful inspection, the dealer called and explained he could not find anything wrong with the engine. The boater explained again what had happened, and the dealer took the boat out on the water for a test run.

On the water, the dealer was able to duplicate the problem. He felt the cause was in the fuel tank. He drained the gas, replaced the fuel line from the tank to the water-separating fuel filter and refilled the tank with fresh fuel. He then asked that the boater take the boat back on the water to verify that the problem was corrected.

The boat captain again took his boat to the water and went for a shakedown cruise. This time the engine would run well up to 2,500 rpm, but if he tried to go above that speed, it would sputter and kill.

Fortunately, the engine would restart, and it ran well as long as he did not exceed the 2,500-rpm mark.

At this point, the boat captain tried an experiment. He got a 6-gallon tank and hose, which he hooked up to the motor. This eliminated the entire fuel tank, fuel pick-up, fuel hose and water-separating system from the engine.

With the 6 gallon tank hooked to the engine, it ran flawlessly for over an hour.

This is one of the easiest tests that anyone can run whenever they feel their engine is having a fuel-supply problem. In this case, the boat owner now knows his problem is in the boat and not his engine. All he needs to do now is trace down that problem and make the necessary corrections.

The e-mail continued by stating that the boat was approximately 15 years old, and the owner thought there may have been trash in the tank that was sucked up into the pick-up tube and caused a restricted fuel flow.

He is considering draining the fuel tank and leaving it open for a few days to evaporate any liquid left in the tank. Then he would use a shop vac to suction up any trash in the tank.

In my return e-mail, I explained to him that this would be extremely dangerous and should not be attempted. First of all it would take much longer than a few days for remaining liquid to evaporate from his tank, and even after the liquid had evaporated, there may still be dangerous gasoline fumes left in the tank.

Shop vacs are not designed to suction explosive fumes, and they are not shielded against spark. He could easily ignite the remaining fumes and the resulting explosion could cause severe injury to him and his boat.

Whenever I’m faced with a fuel-supply problem, I like to start at the tank and work my way back to the engine. In this case, the first thing to do is locate any inspection hatches in the floor of the boat. These hatches usually are located over the fuel pick-up tube and the gas gauge sending unit.

If possible, remove the fuel line from the pick-up tube, and then lift the pick-up tube out of the tank. Now you can inspect the pick-up for any trash. Also check closely the length of the pick-up tube.

Many years ago I worked on a boat with a similar problem. The top of the tank had sagged down with age, and the pick-up tube was resting on the bottom of the tank. The tube had a square cut at the bottom and fuel could not get into the tube fast enough to supply the engine.

The correction for this boat was to simply cut the bottom of the tube on an angle so that even if it did hit the bottom of the tank, it would still supply fuel.

The next thing to check is the hose barb fitting at the top of the pick-up. This fitting is usually equipped with an anti-siphon valve. This valve is there as a safety in case the fuel line should become cut or broken, it will not siphon gas into the bilge of the boat.

Many anti-siphon valves become corroded and restrict fuel flow. If this is happening, just replace the anti-siphon valve.

The e-mailer said the dealer had already replaced the fuel line from the tank to the fuel filter, but no mention was made of the water-separating filter. It is possible for this filter to develop a small pinhole in the outer casing usually caused by rust. This would cause the fuel system to suck air.

Last but not least, the fuel line from the water-separating filter to the engine, including any plug-in connections at the engine, should also be checked. A kink in this line or a pin hole or tear in the hose, or even a worn o-ring inside the plug-in connector, can cause the same sort of problems this boater is experiencing.

Here’s wishing you a summer packed full of many hours of boating fun. If you are experiencing problems with your boat, motor or trailer, you can e-mail me at