Tech Tip: Fuel Line Repair - Hose Job

A few weeks ago I noticed a small fuel leak coming from my Triumph's petcock. Thinking it was nothing more than a loose clamp, I gave it a tweak and more or less forgot about it. Three days later the leak returned, only this time it was more pronounced.

My first thought was to replace the OEM-style spring clamp with a heavy-duty worm drive version, but when I removed the fuel line I found that the inner portion of it had deteriorated to the point where all the clamps in the world weren't going to seal it. As you can see from the photo, the inner portion of the hose had separated from the outer cover, hence the leak.

As to why the hose came apart, I can only guess. Since the problem occurred shortly after some carburetor work was done, I'm going to assume the fuel line was damaged when the fuel tank was either removed or more likely when it was replaced, and the line, which is snug over the petcock nipple, was worked back into place. Once the line was nicked, fuel found its way between the inner hose and the outer cover and began to leak past the clamp.

This isn't the first time I've seen something like this happen, though thankfully it's not particularly common. Typically, when a fuel line breaks up it either restricts fuel flow (check out the flap hanging down and you'll see why) or pieces of rubber break off and plug the carburetor jets. A restriction can be tricky to find, especially since they usually occur only at high speeds when fuel demand is at its greatest, and tend to be intermittent. On the other hand, rubber bits in a float bowl are usually a dead giveaway that something's amiss with the fuel line, especially if they're stuck between the float needle and its seat.

A couple of recommendations here: First, the most likely place to find a damaged fuel line is where the hose is forced over a fitting, so anytime the line is removed from the petcock, fuel pump or carburetor, take a few seconds to examine the inside of the line. If damage is found, replace the hose, or at very least cut it back beyond the damaged area.

Secondly, to avoid tearing the hose use a bit of silicone or WD-40 to lubricate it prior to installation.

Lastly, although fuel line deterioration is rarely a problem, it does happen, especially as the line get older, which is why all manufacturers recommend replacing the lines at periodic intervals. -MZ

Resources

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Tool Box
A bike jack is prerequisite for this job; doing it on a milk crate is asking for trouble.
Appropriate hand tools: sockets, wrenches, plastic mallet, hammer, center punch.
A 3/8th electric drill and a 5/16ths bit. You might want an extra bit in case you dull or damage one.
A pipe cutter to cut the preload spacers to size.
A small rat-tail file to deburr the drilled holes.
You'll also need a drain pan, tape measure, flashlight, lots of rags and aerosol degreaser (like brake clean or electrical contact cleaner).
I'd also recommend installing new washers under the damper rod bolts; you can use OEM or over-the-counter copper or aluminum crush washers.

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