Fuel System Basics
Whether idling through the no-wake zone or cruising across the bay at full throttle, any engine relies on a steady stream of clean fuel. Selecting the appropriate fuel components is easy when armed with a little knowledge of the engine requirements. Engine size mainly determines the size of fuel components required. The larger the engine size and HP, the thirstier the engine and the greater the draw on fuel. Well designed fuel systems are engineered to deliver sufficient fuel flow through the spectrum of engine speeds. Improper components may reduce fuel flow, and like a dam in a river, everything down stream becomes fuel starved, resulting in a rough running engine. Engines excel with quality fuel components like those made by Racor, Sierra and Attwood.
Filtration is the best protection
Crucial to fuel flow is a well maintained fuel filtration system. Properly sized filters should extract contaminants without restricting flow. Marine systems have two stages of filtration, the primary or pre-fuel filter and the secondary, or engine filter. The primary filter is first in line. Its task is to extract water and large particle contaminants, and is therefore serviced more often. Primary filter systems offer dramatically improved protection over a single filter system alone. If your inboard or outboard does not currently incorporate a primary filter, an aftermarket model can easily be installed. Be sure to select a primary filter (also called a fuel water separating filter) that is sufficient to handle the engine flow rate at full throttle. Racor and Sierra each offer a range of easily installed primary fuel/ water separating filters. Next in line are Secondary filters, typically located just before the fuel pump, carburetor or injectors. Secondary filters function as a last chance trap to rid fuel of grit and debris, and are usually specific to OM (Original Manufacturer) and engine model.
To fairly evaluate filter performance, consider not only the smallest particle size a filter extracts, but also the efficiency at which it filters. For example, take two 10 micron filters. Each may filter out 90 percent of all particles 10 micron or larger at half throttle, but when fuel flow accelerates, a high quality filter maintains efficiency while a lesser filter allows far more contaminants to pass through. The efficiency also drops when filters are left in service beyond their usable life. Spent filters not only lose the protective filtration features but also dam the river, starving the engine of fuel. A vacuum gauge installed on the filter will detect the pressure drop caused by a clogged filter.
Fuel Line Ratings Explained
A common question to our sales team is type of fuel line needed. To maintain a solid stream of fuel minus air and obstructions, use marine grade fuel line components. Think of the fuel line rating system like a report card- A1 is the best! It has the highest fire resistance (2.5 minutes open flame) and lowest permeability making it appropriate for any application. Newest evolution is A1-15, which meets new higher EPA standards for ultra low permeation. The EPA standards became effective Jan 1, 2009, meaning any new boat build with gasoline filled hose in confined areas must use A1-15 hose. At Jamestown Distributors, it's safe to assume any A-1 rated hose sold now is the newer A1-15 type.
Ratings are determined on these two factors, permeability and fire resistance. Particularly with volatile gasoline, permeability is a concern due to vapor build up. If it is in an enclosed space "below deck" it must not give off explosive vapors. Manufacturers often refer to hose as "above deck"/"topside" or "below deck" hose, which is simply a trade gimmick way of phrasing the permeability rating.
The rating system exclusively for marine hose is known as SAE J1527 and it provides for grades as follows:
A1--fuel feed hose; has a fire resistant cover; is designed to have fuel in the hose at all times. Least permeable with highest fire resistance.
A2--fuel vent hose; has a fire resistant cover; is not designed to have fuel in the hose at all times.
B1--fuel feed hose; without fire resistant cover; is designed to have fuel in the hose at all times; intended for non-enclosed spaces. Diesel engines or above deck outboard gasoline applications.
B2--fuel vent hose; without fire resistant cover; is not designed to have fuel in the hose at all times. Diesel vent lines.
If you are building a boat or replacing a deteriorated fuel system, buying 1 coil of A1 hose is often the most useful and safest way to go with less leftover hose in the end.
AWAB clamps are the best choice for complete clamping force to secure fuel hose to barb fittings. A vibration resistant screw and a non-perforated inner surface with rounded edges help this clamp achieve a hose-friendly leak-free seal. Use these clamps in conjunction with brass or stainless steel fuel line fittings to connect tank vents, fuel fill hose, deck fill plates, and fuel feed lines. Any new installation must include a fuel line shut off valve. To achieve maximum performance at higher speeds or engine loads, all fittings selected should maintain adequate ID (internal diameter) throughout the fuel line. If not, the narrow diameter hose will act like a kink in a garden hose; the result is loss of power at wide open throttle. For outboard systems, Sierra offers complete replacement fuel lines to fit Mercury, Johnson, Evinrude, Honda and a host of others. They also offer replacement bulbs and connectors to keep outboard fuel lines primed and running.
We also field many questions regarding fuel tanks. The quick synopsis is there exists a difference in diesel and gasoline fuel tanks. The main difference is twofold: the permeability of the tanks and the connection system. As to permeability, outboard gasoline fuel tanks (typically red) are only ever approved for open air use. If you place this tank in a confined chamber (below deck, fish box type compartment, under console) the build up of fumes poses risk of explosion. Therefore, any gasoline tank used housed in an enclosed space must meet minimum permeability regarding fumes to minimize explosive hazard. An acronym seen repeatedly on such tanks is C.A.R.B. (California Air Resources Board) approved. Because California has the most stringent air quality control measures in the country, if a tank is CARB approved it is a good bet it meets standards in every other state. The second point of fuel tanks is the difference between diesel and gasoline tanks. The main difference: the pickup. Gasoline tanks draw fuel out of the tank. Diesel draws fuel out and circulates it back in. This difference means a diesel tank must have outlets for pickup and return lines. Also, diesel is much less volatile than gasoline. Therefore, most tanks that are approved for gasoline could work for diesel if the pickup and return is modified to diesel setup.
Setting up fuel tanks often requires threading in the appropriate fuel barb connector or proprietary quick connect specific to engine manufacturers. If you need to seal threads for gasoline, there are very few thread sealants up to the task. We recommend Aviation Form-A-Gasket No. 3 Sealant by Permatex. This is the same sealant used in aeronautics and marine, and will withstand both gasoline and diesel exposure. Teflon tape is used but not recommended for modern engines. Tape risks sending shards downstream which easily clog injectors and tiny orifices rendering your engine useless. For more on this, see the JD HowTo article How to Properly seal Fuel Fittings and Fuel Lines. If you are working on gasoline engines, or any engine for that matter, it is extremely important to have a qualified marine mechanic inspect or perform the work.