Replacing Stihl Fs85 Fuel Line: A Step-By-Step Guide

The Stihl FS85 is a brushcutter or weed eater that was produced in huge quantities over a number of years. The fuel lines on Stihl engines contain a main or suction hose and an impulse or return hose. These hoses suck gas from the tank into the carburettor, and any excess fuel returns to the tank to be reused. The lines age quickly due to fuel impurities and must be replaced almost every season. Clogged or dirty fuel lines are also the cause of many common engine problems. To replace the fuel lines, first drain all old fuel back into an approved fuel container. Then, pull the fuel filter off the end of the suction hose. Unhook the throttle cable from the choke cover plate and pull the fuel return hose off the stub next to the spacer flange. Cut off two lengths of fuel tubing, slice a 45-degree taper into one end of both lines, and push the suction hose through the main fuel hole in the fuel tank. Coat the grommet on the new suction hose with Stihl press fluid and push the hose down until the rubber lip is properly seated. Finally, coat the stub and end of the return hose with Stihl press fluid and push the return hose until it stops against the stub.

How to Replace a Stihl FS85 Fuel Line

How to drain old fuel from the STIHL FS85

To drain old fuel from your STIHL FS85, you will need an approved fuel container and a metal hook (baling wire).

First, open the fuel tank cap and drain all the old fuel into the approved container. You can do this by removing the fuel filter at the bottom of the tank with the metal hook and pulling it off the end of the suction hose.

Next, remove the air filter cover, the air filter itself, and the two mounting screws holding the air filter box in place. Then, remove the choke cover plate on top of the carburetor and unhook the throttle cable from the choke cover plate.

Now you can pull the fuel return hose off the stub next to the spacer flange and pull the fuel suction hose out of its seat on the carburetor. Pull both lines out of the engine and dispose of them.

Once you have drained the old fuel and removed the old fuel lines, you can replace them with new ones.

Removing the fuel filter

To remove the fuel filter from your Stihl FS85, you'll need to open the fuel tank cap and drain all the old fuel into an approved fuel container. You can then pull the fuel filter at the bottom of the tank upward, using a metal hook. Once it's loose, pull the fuel filter off the end of the suction hose.

Now you've removed the fuel filter, you can move on to replacing the fuel lines. To do this, you'll need to remove the air filter cover and unhook the air filter. Remove the two mounting screws holding the air filter box in place, and then remove the choke cover plate on top of the carburetor. Finally, unhook the throttle cable from the choke cover plate.

Disconnecting the air filter

To disconnect the air filter on your Stihl FS85, you'll need to follow a few steps.

First, remove the air filter cover. This will expose the air filter and allow you to access it for disconnection.

Next, unhook the air filter. Depending on your model, there may be some mounting screws holding the air filter box in place, so be sure to remove these with the appropriate tool if necessary.

Now, you can lift the air filter out of its housing. Be careful not to damage the filter or any surrounding components.

Additionally, you may need to disconnect the throttle cable from the choke cover plate, which is located on top of the carburetor. This will ensure that the air filter is completely disconnected and free from the engine.

Finally, if your model has an air filter cover or housing, you will need to remove this as well. This will typically have a few screws holding it in place, which you can remove.

By following these steps, you should be able to successfully disconnect the air filter on your Stihl FS85. Remember to refer to your owner's manual for any model-specific instructions or variations.

Cutting the new fuel tubing

When cutting the new fuel tubing, it is important to ensure that the tubing is the correct size and length, and that it is cut cleanly and accurately to prevent leaks and ensure a secure connection.

Firstly, you will need to measure and cut two lengths of fuel tubing, each about 6 inches long. A tubing cutter is the best tool for this job, as it will provide a clean, straight cut without jagged edges, sparks or shavings. Tubing cutters are available in various sizes, so make sure to select one that fits the tubing you are using. You can find them at any hardware store or online. If you do not have access to a tubing cutter, a fine-tooth hacksaw blade or a pair of snips can also be used to cut the tubing, but be very careful to avoid creating any sparks, which could be dangerous when working with fuel.

Once you have cut the tubing to the correct length, the next step is to slice a 45-degree taper into one end of each line. This can be done with a sharp knife or a tubing cutter, if it has an angled cutting option. This tapered end will help to guide the tubing into the correct position when you are assembling the fuel lines.

Now you have your new fuel tubing cut to size, you can proceed to the next step, which is feeding the new suction hose into the fuel tank.

Inserting the metal wire into the suction hose

To insert the metal wire into the suction hose, you'll need to first unbend the hook in the metal wire. Once the hook is straight, insert the wire into the suction hose. It's important to ensure that the metal wire is pushed all the way through the hose.

After the wire is inserted, push the hook and suction hose through the main fuel hole in the fuel tank. Once this is done, you can withdraw the metal wire, leaving the suction hose in place.

The next step is to coat the grommet on the new suction hose with Stihl press fluid. Push the fuel suction hose down until the rubber lip is properly seated and the flange on the hose lies flat against the fuel tank.

This process will ensure that the new suction hose is securely in place and ready for the next steps in the fuel line replacement.

Frequently asked questions