outboard motor parts

DIY inboard outboard boat motor parts & accessories

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The fuel system on inboard/outboard boats in most cases, is very similar to that of automotive applications. Fuel tanks, fuel pumps, fuel filters, and carburetors are commonly used, although the introduction of fuel injection has become very common in the last few years. In this section, we will be looking mostly at conventional carbureted applications due to the fact that most fuel injection applications require special tools and analyzers to troubleshoot.

Fuel Tank

Fuel tanks come in various sizes, are made of either polyethylene(plastic), aluminum, or steel, and may be located in different locations depending on the application. There are only about three things concerning the fuel tank that could cause problems.

First off, corrosion or presence of moisture can obviously clog filters and carburetors, so regular observations for such should be performed and appropriate action taken if found.

Secondly, the fuel sender (if equipped), Figure 1, is located on the top of the fuel tank, attached usually with 5 small screws and contains a gasket seal. A ground(black) wire and sender(pink) wire are also attached to the fuel sender. The sealing gasket should be periodically checked for leakage, and the wires should be checked for corrosion at connections. If you experience a problem with the fuel gauge, 8 times out of 10, you will find that the fuel sender is the culprit. About the only way to check the sender is by removing it from the tank, and knowing that a good hot and ground exist at the fuel gage, swivel float arm of fuel sender manually, and if fuel gauge needle does not move, it most likely means that the sender is bad. Senders are pretty much a universal standard, the only real difference being the length of the float arm. Replacement senders can be acquired that come very close to your original, and can be slightly modified by bending the arm to match the correct length and swing function of your existing sender.


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Last thing on the fuel tank would be the inlet and vent hoses. The vent on a fuel tank can sometimes become kinked or clogged. If you experience a "running out of fuel" type condition, check to make sure that your vent hose and fittings are not closed off in any way. If the fuel tank cannot breath, it will cause a reverse suction condition and prevent fuel from getting to the motor. The inlet hose and fittings should be checked periodically for leaks.

Fuel Pump

The fuel pump of an inboard/outboard can be either electrical(on most newer applications) or mechanical. A fuel pump usually either works, or doesn't, but occasionally, they can develop a weak pressure condition from worn diaphragms. Most inboard/outboard fuel pumps also contain a saftey valve in case of diaphragm rupture. Figure 2 In this situation a hose connected to the fuel pump routes the fuel to the carburetor to keep fuel from collecting externally in the engine compartment. A ruptured diaphragm is pretty rare, but the hose mentioned(usually a 1/4" yellow tinted color) should be checked for good condition just in case this ever DOES happen.

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Fuel Filter

The fuel filters on inboard/outboards can contain different configurations. Some filters may be located on the fuel pump, some applications use whats called a water separator, Figure 3A and most have a filter at the carburetor. These filters should all be changed on an annual basis, and special attention should be given to a water separator application to gauge moisture and corrosion content of fuel system. If excess corrosion, moisture or water content is evident, take appropriate measures to prevent the building breakdown of operation. This is an easy and inexpensive procedure that most people overlook, and can prevent costly carburetor repairs.

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Carburetor

Carburetors are probably more in use as of the moment than is fuel injection applications. About the only thing the average person can do with fuel injection is to regularly replace fuel filter. As mentioned in the beginning of this section, fuel injection systems require special tools and analyzers to troubleshoot. Carburetors mostly come in either 2 barrel, Figure 4 or 4 barrel models, Figure 5 although some small engines may contain multiple single throat carbs.

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As far as maintenance, the fuel filter should be changed annually, but there can also be other problems that can develop. Most commonly, you may experience 3 different problems with a carburetor.

If you experience a "bog" condition when attempting to accelerate throttle, it usually is a sure bet that the accelerator pump Figure 6 or fuel squirter passage of the carburetor is worn or clogged. In this case the top or bowl of the carburetor sometimes can be removed and accelerator pump could be replaced. This is not always the best choice of repair due to passageways that may possible be clogged with sediment. In this case, carburetor must be removed and disassembled to correct the problem. In this instance, it is advised to go ahead and do a complete rebuild of the carburetor at that time, and assure that all internals of carburetor are clean and in good adjustment/working order. Most all carburetor rebuild kits contain full instructions and settings for rebuilding your specific model and type of carb.


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Cold starts with inboard/outboard motors can be easy or hard, depending mostly on the condition of the choke. Some applications contain a mechanical temperature activated choke, and others use an electrical type activation. Either way, the choke must be clean and in proper adjustment for the environment it is being used. The choke linkage should be inspected occasionally for any obstructions or "sticky" operation. The choke flapper on the carburetor Figure 7 should be readjusted periodically to ensure proper operation. Flapper is usually adjusted by turning adjustment housing of choke so that flapper completely closes to the carburetor bore, and an ever so slight costive pressure beyond fully closed is obtained. The choke pulloff will take care of further proper positioning of flapper required for easy starting of cold motor.

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Finally, the air/fuel mixture setting of the carburetor should be checked annually or sooner if problem occurs. The air/fuel mixture is adjusted with metering type screws and can be located either on the front of the carburetor base, or and the side/s of the carburetor metering blocks. Refer to the recommended settings for your specific application for this procedure.

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If you should have any questions about your fuel system that may not be answered in this section, feel free to email us. We will gladly help you in any way that we can.