Replacing Fuel Lines in a String Trimmer

Ethanol in Gas

The addition of ethanol in gas has been a major problem with small engines, such as string trimmers. In the US, almost all gas pumps have a 10% ethanol blend. A major issue is that it has a tendency to break down rubber, resulting in discoloration and cracking of the fuel lines. If this occurs, replacing fuel lines is the only fix. Fortunately, replacing fuel lines in a string trimmer or other small power tool is not very difficult.

Ethanol is a corn-based alternative fuel. It’s cheaper and more stable (higher octane) than gasoline, but has a lower energy density. High-ethanol blends such as e85, which are 85% ethanol, thus lend themselves well to forced induction applications, where the high octane is desirable to prevent pre-ignition.

For the average consumer, ethanol is less desirable. Because it is less energy dense than gasoline, it results in worse fuel economy. It also has a tendency to attract water, so it is more prone to going bad from sitting than gasoline. Fuel stabilizers, such as Stabil, can help with this issue.

As a final aside, because it is prone to collect water and rot your fuel lines, it is recommended to drain ethanol gas from small outdoor power tools. I tend to drain my string trimmer’s tank in the fall and then run it out of gas before storing for the winter. It seems like too much of a pain to do this every week. This worked fine until I forgot to do it last year. My chainsaw, on the other hand, sees less use, so I always empty it after use.

Symptoms of bad fuel line

So how do you know if your fuel line has gone bad? It can discolor. My trimmer has a clear green-tinted line that had started turning brown. It’ll also become fairly brittle, and you may be able to pinch the hose and see cracks. The primer bulb also won’t seal properly, so you’ll notice more air than usual when you try to prime the trimmer. Lastly, it may not rev up properly when you give it throttle. At higher throttle, it may suck air instead of gas, leaning out your fuel mixture.

If replacing the fuel lines doesn’t work, the other likely culprit is your carburetor. As I describe in my article on replacing a string trimmer carburetor, it’s cheap and easy to buy a remanufactured unit and drop it in. It is worth starting by at least inspecting the line for cracks, though.

Getting replacement fuel line

Easy mode: Home depot sells a “fuel line kit” for Echo trimmers

There are a few ways to go about getting replacement fuel line. The easiest and most expensive is a kit, such as the one pictured. This one costs about $11 at Home Depot, and is a drop-in replacement fuel line for my Echo GT-225, among other string trimmers. Most brands offer something similar. Replacing fuel line in a string trimmer this way is very easy, as everything is already cut to length and ready to go. It also includes a replacement fuel filter, which is usually a couple of bucks by itself, along with a primer bulb and gas cap seal. If you need a carburetor as well, you can buy all of it on Amazon for about $22.

You can also buy a spool of universal fuel line for $4 or so. This will work as long as it’s the right diameter. Simply cut off pieces of tubing to replace what you have. I went the easy route.

Removing the old fuel line

Completely remove the gas cap

The first step is to completely remove the gas cap. After unscrewing it, this trimmer has a plastic circle that you can pinch and remove.

Unplug fuel lines

Then, you can unplug the fuel lines from the carburetor. One line will bring gas to the carb, and the other is a return. These lines look new because they were from an attempt to use some scrap tubing from replacing the wiper hoses in my car. They weren’t quite the right size, although very close.

Push the grommet down into the tank

With the fuel lines undone, you can push the grommet holding all of the fuel lines down into the tank. It can also be pulled out, whichever way works easier.

Pull the grommet and lines up through the fuel fill area

You can then reach down through the fuel fill area, snag the lines and grommet, and pull the whole assembly out. This will include the fuel filter attached to the end of one of the lines. If it’s hard to reach, a bent coat hanger works.

Replacing the line

Feeding fuel filter in

If you are using universal line, you should at this point cut off pieces of tubing and replace the pieces you just pulled out. In the case of this string trimmer, there is one line in the tank, attached to the fuel filter, and there are three lines outside of the tank. Two of these go to the carburetor, and one goes to a vent. There is also a male-male hose adapter connecting the inside line and one of the outside lines. You can probably reuse this as long as it hasn’t cracked.

If you have a pre-made kit like this, you can begin feeding the fuel filter into the tank as shown. If your fuel filter won’t fit, you can try to put it back in through the fill opening, but it’s difficult to get the grommet back through from inside the tank. Alternatively, you can keep the fuel filter off for now, and put it on the line after the grommet is in place.

Seating the grommet

The grommet should be able to be pushed into the tank as shown.

Done

Once you get the grommet fully seated, the job is nearly done.

Fuel lines to carburetor

The final piece is to reconnect the two fuel lines to the carburetor. On my trimmer with the factory colored lines they connect as shown. Now, you may have forgotten the order in which these connect. If you do, it’s no big deal: just take a guess and attempt to prime the trimmer. If the bulb won’t fill, you need to switch the lines around.

Replacing the gas cap gasket (optional)

The gasket inside the gas cap

Simply pulls off with a screwdriver or this paint can opener

This step is totally optional. There is a gasket under the fuel cap that my kit included. I figured that I may as well replace it. To do this, simply pry the old one off and slide the new one on.

Wrap-up

Today’s increase in ethanol-blend gas can damage your outdoor power tool fuel lines. Fortunately, replacing fuel lines in a string trimmer or similar power tool is pretty easy. It’s not a bad idea to try to seek out 100% gasoline; there are websites that can help with this. Also be sure to completely empty your trimmer of ethanol-blend gas, even if it has Stabil in it, when it is going to sit for any significant period of time.

If your trimmer is dying and replacing the fuel lines didn’t help, you may need to repair or replace the carburetor. Fortunately, complete replacement carbs are now available online for $15-$20. I’ll document doing this on my trimmer in a coming article.