How to Check the Outboards Fuel-System Components?

Despite the whirlwind of advances in outboards in recent years, virtually every outboard installation shares one throwback to simpler times — a fuel-line primer bulb. Although some of the newer engines don’t require the manual priming that used to be mandatory when first starting a cold outboard, it’s comforting to know you can always give the old’ bulb a little CPR to get fuel flowing from the tank to the engine.
As a result, primer bulbs are located where they’re easy to get to — and that typically means an exposed location, often in the splash well itself, where the bulb is subject to deterioration caused by extreme heat and cold, the sun’s UV rays, simple age and even additives (such as alcohol) used in today’s gasoline.
Outboard fuel lines suffer from the same ravages and, over time, can become brittle and crack.
Although fuel-system components can take surprising abuse, common sense dictates regular inspection. After all, cracking or leaking fuel lines are an extreme hazard, so this is one point of maintenance you really shouldn’t put off. What’s more, if a primer bulb splits, you may not be able to start your engine — or keep it running.

CHECK CLAMPS, TOO

Outboards Fuel-System

Besides a visual once-over to look for cracking or other signs of deterioration, check the pliability of the bulb and related fuel lines. If anything seems brittle, it’s time for a change.

While you’re at it, inspect all hose clamps to ensure they haven’t loosened up, and also look for signs of rust. As experienced skippers well know, it’s not uncommon to have a stainless hose clamp equipped with a ferrous-metal screw; and while the clamp holds up to the marine environment, the screw rusts away and lets loose.
Fortunately, replacing primer bulbs and fuel lines is a simple and inexpensive job, so it pays to play it safe and immediately swap out any components that are suspect. The swap can be a piece-by-piece affair, or you can buy a ready-made fuel line/

primer bulb assembly and install it in minutes.

BY THE NUMBERS

Outboards Fuel-System
We went the latter route — but took the opportunity to do a little custom fitting for our application. Follow along as we walk you through the process on a project boat rigged with twin Mercury 150s.

But first, regardless of whether you’re putting together your own system or using a ready-made assembly, be sure the materials are properly rated for the job, per U.S. Coast Guard and SAE J1527 standards. In addition, make sure the interior diameter of the fuel line will provide sufficient flow to your outboard (if in doubt, consult the engine manufacturer).

We replaced the fuel lines and primer bulb for each engine using Tempo (440/248-1450; tempoproducts.com) Part No. 180194 (Mercury equivalent 32-827927A). By a few dollars, this OEM replacement kit was the priciest of the three options available to us. The least expensive route would have been to purchase a universal 3/8-inch-diameter fuel-line assembly, which offers slight savings over piecing together the individual lines and bulbs. Even so, we think we came out ahead on the deal.For starters, the original Mercury fuel-line-to-engine connectors appeared in less than stellar shape, so we felt better about replacing them with fresh hardware. Secondly, even though we didn’t need the kit’s quick-connect fittings that attach to a portable fuel tank, we saved them for occasional use when we want to carry portable tanks on deck to extend our boat’s range. Considering that each of these fittings can sell for upwards of $10, we made out like bandits.

STEP 1: After years of UV exposure, the old fuel lines had become stiff and were difficult to remove. After slicing a short portion of the hose, we used a screwdriver to carefully separate it from the nipple fitting at the water-separating fuel filter.

STEP 2: Only use U.S. Coast Guard-rated fuel hose aboard boats. The old 5/16-inch line was not in tip-top shape, and lacked the pliability and flow capacity of the 3/8-inch replacement line.

STEP 3: Mercury’s quick-connect bayonet fitting is located near the front cowl latch. In this trio, it’s the center fitting, surrounded on the right by the replacement Tempo 486MFC (Part No. 220143 or Mercury 22-13563A3) fitting. On the left is the Tempo 482MFC portable tank connector (Part No. 240061 or Mercury 22-13563A7), which can be distinguished by its larger alignment hole.

STEP 4: Since the feed end of the fuel line would attach directly to the hose barb at the water-separating fuel filter, we cut off the remote tank fitting and saved it for later use. This also allowed us to shorten the hose to suit our installation.

STEP 5: As seen here, the hose leading from the primer bulb to the engine was also too long for our application. We trimmed it for a custom fit, then used the excess hose to replace the “loop line” leading from the bulkhead fuel barb to the “in” fitting on the water-separating fuel filter

The final step was to secure the new bayonet fitting with an all-stainless hose clamp. Ideal’s No. 6260653 was the right fit — it had enough teeth to let the screw bite, but no protruding straps to cause cuts.

Next, we primed the fuel bulbs, checked for leaks and then, using a garden hose and earmuffs, the test started the engines. Everything ran A-OK… so I guess we’re ready for more primetime on the water.

What’s It Take?

Outboards Fuel-System

The cost of rebuilding your outboard’s fuel line system depends, naturally, on how many components you actually swap out. If the fuel lines leading to and from the primer bulb are in good shape and all you need to replace is the primer bulb itself, you’ll only have to spend $12 or so for a new primer bulb (plus the cost of stainless hose clamps, at around $1.60 apiece, if needed).

U.S. Coast Guard and SAE J1527-rated, 5/16-inch-diameter fuel line sells for approximately $2 per foot. The slightly larger 3/8-inch line costs a few cents more but offers greater flow volume — a definite plus for more powerful engines. Unless it’s in questionable shape, plan to reuse your outboard’s line-to-engine connector fitting.

Universal fuel line/primer bulb assemblies (sans fittings) are available for $16 to $28, depending on hose diameter and length. Alternately, you can purchase complete white H4 led bulb headlight assemblies that include the fuel line, primer bulb and quick-connect fittings that attach to the outboard and a portable fuel tank. Prices vary depending on the application, but the Tempo/Mercury setup we used retails for around $23. Since our boat had twin engines, the total cost was approximately $46.

Timewise, it’s a pretty quick job. Even if you’re custom fitting the system, once you’ve got all the components lined up, the swap shouldn’t take more than 10 or 15 minutes per engine.

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