The grass is getting tall after our warm beginning to spring. Time to get the old string trimmer out and give it a once over. We will be using the Stihl factory tune-up kit part number 4144-007-1800:

First order of business is to remove the cover over the air filter. Using the modern Stihl scrench or T-27 Torx bit unscrew the cover.

This will expose the air filter and carburetor housing.

Remove the old air filter.

Now we see the serpentine style intake manifold for the unit. I noticed some oily buildup so I removed the black intake housing cover.

I used a rag to remove the oily buildup inside the intake manifold.

After cleaning the intake and putting the manifold cover back on, the new intake filter was installed.

The next step is to replace the old fuel filter. I must admit on many of my older tools I never took the time to replace this part. It was always difficult and I never had trouble with my older Stihl units. That being said, modern blends of gas here in California are not kind to small engines and I am harder on my tools than I used to be lends me to replace this part every year on all my tools.

Start with opening the cap to the gas tank. Locate the fuel filter.

I prefer to use a pair of assembly tweezers my dad left me to grab the fuel line right before the filter housing. This lets me move the filter and hose around without fear of slipping. A pair of hemostats would work nicely too, provided the grip surface isn’t aggressive enough to damage the fuel hose. My assembly tweezers have a mild knurling on them.

Move the fuel filter in such a way as to pull it out the opening. This is the tricky part. The fuel hose is flexible enough to come out with the filter without worry about damaging it.

Replace with new filter and push it back into the gas tank.

The last part of this tune-up is replacing the spark plug. A 5/8″ deep socket is required to remove the plug. I use a simple spark plug gapper to check the gap of the plug from the factory. I find that all the plugs vary in gap specifications and so I like to re-gap them to exactly what the spec sheet says.

In this case this new plug gapped to over .025 thousandths, so I re-gapped to the manual spec of .020.

Remove the spark plug wire via the boot, exposing the plug.

Remove the old plug with the 5/8″ deep socket. My old plug was pretty well fouled. Partly due to me using old gas mix. The guy at the local saw shop has since recommended that I only use 91 octane fuel mix and only a month old or less. He says he has seen the ethanol blend here in California start to deteriorate after that amount of time and can potentially damage engines.

Replace plug and torque to spec on the plug, around 20 N-m. Reinstall the boot and let her rip.