Fuel System Tips

So how is your engine running these days? Many boaters, myself included, often go days or weeks without thinking about that. But from time to time, the motor will hiccup or stumble and will remind us that it if we let her get too far from our mind, she’ll eventually get fed up with the inattention and let us down.

Hopefully, you’re also like me, and you don’t let it get that far. You do pay attention more often than not. You take time to check the fasteners, lubrication points, engine temperatures or the coolant indicator stream. What I mean is you take time to show her you care, right?

When it comes to your motor, there are certain necessities that you cannot overlook. You’ve got to see to its mechanical needs. This includes items like fasteners and anodes, but probably most importantly, this involves lubrication of wear or friction surfaces. And you’ve got to make sure she gets the power she needs, so the electrical systems from the charging and starting systems to the ignition systems must be kept in good working order. Luckily, there is not a lot of maintenance involved with electrical systems. Maintain the battery, make sure the wiring harness and connection are not damaged or corroded in any way.

But, off all your boat motor’s needs, arguably the MOST important is your engine’s need for fuel. I mean, at the end of the day, if there is no gas, there is no go, right? So the care and feeding of your fuel system should be a primary concern.

And again, thankfully, there is not a whole lot of necessary maintenance that your fuel system demands. First off, make sure you keep the fuel tank filled with fresh, high-quality fuel. If the fuel in the tank is old, stale or contaminated, then the motor will not run properly. If you leave untreated fuel in the tank for more than a month or two, evaporating hydrocarbons will eventually render the fuel almost useless. And, if the fuel evaporates from the float bowls of the carburetor, it will leave behind a gum-like material that can plug sensitive needles, jets and passages.

It’s funny, but some people are under the impression that carburetor tuning is a regular maintenance task. But honestly, it’s not. The idle or high-speed mixture screws should not require any attention unless something major has changed, like the motor or the carburetor was rebuilt.

If the motor was running correctly before it was put into storage, but doesn’t run right immediately after removal from storage, the fuel supply and fuel system are probably the first places I’ll look. And, this is true even if the motor ran correctly for a few outings. Keep in mind that gum or varnish which forms inside an improperly stored carburetor may take a few hours of operation to brake loose and suddenly clog a passage. Therefore if an engine performance problem pops up early in the season, you MIGHT want to look at the fuel system.

But when you do, don’t immediately decide to adjust the carburetor(s) or don’t immediately suspect the fuel injection system. Again, these are the LEAST likely causes of the problem. When troubleshooting the fuel system, take the same steps that you should take when troubleshooting anything else. Start with the easiest items to check and the least expensive items to fix.

Problems that occur only at idle or only at high speed or load can easily be traced to the fuel system. But before digging into the carburetor or fuel injection system ALWAYS eliminate the fuel supply first.

If fuel starvation is a symptom first suspect the tank vent, and the quickest way to eliminate that as a possible problem is to operate without the tank cap installed or closed.

Another easy diagnostic method that can be used to eliminate problems with the fuel tank, pickup and lines is to operate the motor on a “diagnostic” tank. Obtain a portable marine fuel tank and hook it up to the motor, bypassing the usual fuel supply. Whether or not this eliminates the problem, you’ve already narrowed it down by half the possible components. If the fuel pump is suspect, use a diagnostic tank that also has a fuel primer bulb, when the problem occurs, have an assistant pump the bulb repeatedly, which will in effect duplicate the action of the fuel lift pump. Again, if the problem goes away, you’ve got your culprit.

If you’ve decided it is time to change or clean the fuel filter, there are a couple of basic types which are all easily serviced or replaced. Most motors utilize some form of an inline filter either between the fuel tank and pump or between the pump and carburetor(s) or fuel injection vapor separator tank.

Some inline filters are solid metal or clear plastic housings which are clamped in the middle of two fuel supply hoses. This style is easily removed and replaced by undoing the clamps and carefully pulling the hoses free of the filter inlet and outlet nipples.

Other inline filters consist of a 2 piece plastic or metal housing where a fuel filter bowl can be removed from a filter cap. The bowl often threads into position or is secured by a knurled knob which can be loosened by hand in order to remove the bowl. Inside the bowl or cap of this style filter you’ll find a removable filter screen. If the screen is not damaged it can be rinsed in solvent and air dried (or VERY carefully blown dry using low-pressure compressed air). When in doubt, this type of filter screen is easily and inexpensively replaced.

Finally, many boats and some motors are rigged using a disposable spin-on fuel filter or fuel filter and water separator. These filters resemble automotive oil filters and are removed or installed in exactly the same fashion. Often you’ll want a strap or cap wrench for removal, as they tend to get stuck in place after a season’s use. Once unthreaded, you’ll normally find a small rubber gasket which again looks just like the gasket on an oil filter. Before installing a replacement spin-on fuel filter, be sure to lubricate the rubber gasket with a small dab of engine oil (again, just like with a spin-on oil filter) to ensure a good seal and to help make sure the filter comes off with ease next time you need to replace it.

Many fuel tanks will contain a sock or filter over the pick-up. These filters are usually life-time components, but they can normally be accessed and changed by removing the fuel pick-up from the tank. Similarly, many carburetors or even some outboard fuel pumps may contain internal fuel filters which are not periodically serviced, but which should be given attention during overall or if you’ve encountered a severe fuel system contamination problem. For details on servicing carburetors or fuel pumps, you’ll need a good repair manual (such as a Seloc).

Only after you’ve eliminated the fuel supply, the fuel tank, vent, lines, filters and pump, should you suspect the carburetor or the electronic/electro-mechanical components of the fuel injection system.

So what’s the morale of the story? First, don’t let a little hiccup lead you down the road to the carburetor or the Engine Control Module (ECM). And second, don’t let the fuel supply get so old that it hiccups in the first place.

Fig 1. Arguably the most important need your engine has is for plenty of fresh, clean FUEL, so always make sure you’ve got a good fuel source

Fig 2. If you suffer from fuel starvation systems, first make sure your tank vent is open (if manual) and is not clogged

Fig 3. If you’re uncertain about the condition of the fuel vent, try operating the motor with the fuel cap removed

Fig 4. In the case of built-in fuel tanks, simply open the fuel door and test run the motor to see if this relieves a fuel starvation problem

Fig 5. If you are uncertain about the fuel supply, tank and delivery lines, another quick-check is to run the motor on a separate portable “diagnostic” tank. This tank can be temporarily rigged to supply an outboard, inboard or stern drive, quickly eliminating half of the fuel system components from your troubleshooting

Fig 6. Before checking the fuel pump, make sure you’ve got clean fuel filter/water separators