So you own a Stihl FS 91 R trimmer. Hey, congratulations! This is an awesome machine. Today
we're going to go over what you need to do to get the most out of this machine; have a long life,
enjoy it, don't be disgruntled by it in 2 or 3 years down the road because maybe you haven't
done something right. The FS 91 R is a 1.27 horsepower professional string trimmer from
Stihl. It features a solid Stihl drive shaft so it's going to allow us some opportunities in the
future to do all kinds of different stuff like potentially run a brush blade, maybe put on a
gear box attachment. So we'll cover some of that stuff today, as well as the general maintenance
and the proper fuel and care of this machine. So let's start really quick with the basics;
the basics as far as when it comes to what kind of fuel should I run? What should I put
in this machine? So this is a two-cycle machine. It's gonna run mixed fuel, and we're gonna do
that one of two ways (probably not both of these ways all at once, that might not work very good).
One is buying this Stihl HP Ultra oil and they're gonna sell this in different sizes. These little
guys right here are for a one gallon can, and I always recommend the smaller bottles. I want
to go through my gas. So one of these bottles to a one gallon can, and not just normal gas,
not just any gas. If you can please please please get ethanol-free fuel! So fuel starts going bad
fairly quickly, and the fact that it has ethanol in it just causes all kinds of problems. So
ethanol-free, one gallon with one of these bottles, and I try to do that personally every
couple months. You can go a little bit longer, but really, we want to be flowing through our fuel.
The ultimate though is checking out this Stihl MotoMix, and this stuff is 93 octane,
ethanol-free, it is blended, it is engineered for Stihl equipment, it's engineered for long life.
So this is this a fuel that once I crack this lid, I actually have a 2 year shelf life. Amazing fuel.
It's expensive; I'll own that. And I hear it all the time or I see comments, "I'm not buying that!"
Okay, I get it! I respect it. So during the season there's a lot of people that this is
what they run. And when I say during the season, you know: April, May, June, July,
August, September...October...and maybe October. And then they're thinking, "Man this thing's going
to be done. I'm done with it for the year; the weeds have stopped growing. I'm not weedeating
my lawn every week or every other week." Hibernate with this stuff at least. You want to run this all
year? Awesome! But come the off season put in the MotoMix. So that's fuel. We always need to make
sure we're running mixed fuel and fresh fuel, otherwise down the road, it's going to kick us
in the butt. We're going to have a carburetor problem. You're going to come in, it doesn't
want to start, or it will only run if the choke is on. I'm just trying to help you avoid that.
Let's put some fuel in, let's start this up here a minute. Let's see what we've got to do to start
it up. So I'm going to take the cap off, and the cool thing is you bought this at your local
dealer so there's already fuel in it so you're not doing this first out of the box run. I'm
going to use some MotoMix in here today...get a little bit in. And this is going to have happened
here at Carl's Mower and Saw; our opportunity just to fire it up and make sure it's right. Believe it
or not, every once in a while we have a machine that comes out of the box and it's not perfect.
It's man-made; we fail at stuff. So I have fuel in the tank, I've got a primer. I'm going to
push this primer a few extra times this time, but generally speaking I pump it 4 or 5 times.
Pushing this primer a million times is gonna waste a lot of time but it's not gonna hurt anything so
really 4 or 5 pumps is kind of the right number. But don't worry if you if you get more than that;
you're not going to flood it or cause a problem. And we have this choke right here, and on this I
push in and I rotate (depends where I'm standing) I rotate counterclockwise and that sets the choke.
Turning it on: it's always on, it's always ready to start. So I've got a stop button right here
and I push it and it kills it, but it pops back out and it's ready to start again. So prime it,
choke it, don't have to do anything with the stop button. And a little tip: this throttle trigger
is attached to the choke, so when I squeeze the trigger (hear this click?) that shut the
choke off. On the older Stihl equipment and on a lot of other brands of string trimmers,
when you go to start it you actually squeeze the throttle trigger and it
makes it start easier. It's a little tip/a little trick. So if you've got an old Stihl
and it's starting hard, squeeze the trigger. On these newer ones with the choke that's attached
to the throttle, don't do that because that knob is already doing that for you.
I'm going to grip it right here but before I do that, back up. We've got to be safe;
we're going to get this machine out, we're going to go crazy, we're going to be throwing stuff, so
let's have our safety glasses on. I'd usually take the sticker off otherwise it creates a blind spot,
and let's get our ear protection on. These things are loud and you're going to be out there for a
long enough period of time, you don't want to damage your ears (and I'm starting to speak
from experience because I've ran enough stuff). 1 of 2 things: we can put this on the ground and
hold it down and pull it. People will kind of place their knee somewhere around here.
Or hold it something like this-- probably not approved because I'm going to have a spinny thing
that I'm not in control of, so best to put it on the ground. I'm going to hold it in the upright
position so you can kind of see how this goes. This is a first start; this is fresh out of the
box. My guess is it's going to take a couple extra pulls. Sometimes we're surprised. So here we go:
1-2- and we fired. As soon as it started I hit the trigger, and that shut the choke off.
There's a running FS 91. I shut it off (I don't want to make too much noise in here).
When I'm out there running this i want to run it hard. There's times where I need
to go lightly. You know, working around the roses, next to the fence, around the tree...
tree trunks, so I'm not ripping them up and damaging the trees. But run this hard;
it likes to run hard. Maintenance. You've just got it so you don't need to worry about
anything right away except for really good gas and that, but we do have an air filter.
And that air filter is placed right under here. Your machine came with this fancy tool.
This will take the spark plug out, this end is going to take all kinds of stuff apart. Son't
go too crazy. You know there's some stuff that you're going to want to use it for. Maybe I want
to move the handle up and down? That's nice. Maybe I want to move where the shoulder strap
keeper is up and down? Maybe I want to get to the air filter?
So I'm going to come in here set this down, spin off the air filter cover here.
How often should I check the air filter? That's a good question. You know if I'm out on a dry day,
this thing is sucking in a ton of air and it's probably not going to get filthy nasty all in
one day, but I'd make make a habit out of checking this once a month maybe. Maybe you're not using it
enough to justify that, but the key is is to get into habits. Something that that makes us do it
on a certain schedule. If I don't have a schedule I'm not gonna do it, and then 3-4-5 years down the
road you're gonna bring this into Carl's and it's not running well...and this filter is just nasty.
It's growing mold, there's grass, there's some fuzz growing on, you're like, "What's going on?!"
You should have checked it. So this paper filter is just going to pop out, I'm going to move it
away from the machine, I'm going to tap it on the ground. Can I see good light through it or is it
saturated in fuel or oil or moisture somehow? It's really critical that this air filter breathes.
Let's put that filter back in. So air filter maintenance. We have a spark plug on here and
those spark plugs. they fail/they foul out. But not very often. Again, like my air filter,
I'm probably going to replace it. Is that once a year? Probably a little too often, but it
never hurts to replace the spark plug. And the spark plug on these
is going to be right under here, so I'm going to pull this screw out and I'm going to pop the hood.
We're going to see two things. One is going to be the spark plug boot. Be careful; I see
a lot of people rip these spark plug boots off. They just come in and they pull and it actually
pulls it off of the wire and it creates more of a problem. So when you go to take this off,
you want to kind of shake it/wiggle it out slowly, or sometimes that doesn't work and you're going to
take something like this and just sort of pry it. And now I've got my spark plug boot off and
my spark plug is accessible. Again, with the tool that it came with,
and I can simply take that out. If you pull it out and it looks beautiful, pop it back in. Like
I said, once a year is probably too often but it doesn't hurt to to check it or replace it.
And then right here, this little screw, probably don't mess with it. But under here are the valves.
This is a four-stroke engine running on mix oil so don't mess that up, but at some point
in time these valves are gonna need adjusted and traditionally it's between 125 and 150.
How am I gonna know how many hours do I have? Well there's 2 ways:
1 is maybe I got this cool Stihl Smart Cconnector that connects to my phone (that's bluetooth)
that keeps track of the hours and the maintenance. Pretty cool tool! If you haven't checked this out,
check out the Stihl Smart Connector. The other way is the pull. Right now this pulls
very easy. As those valves come out of adjustment, it will tell you. That pull will become
"chunkier;" you'll feel more of the compression on the compression strokes. So keep an eye on
your pull. When that pull starts getting a little stiff/a little harder, time to adjust the valves.
Wet's move on down here. Not a lot to do in this area although there is a little screw
hiding right under here that allows me to adjust the throttle cable as it stretches. So over time,
this throttle cable that's running from here up to the carburetor is gonna stretch and I can simply
put a little screwdriver in there and turn it clockwise and tighten it up. This is where my
shoulder strap (this came with the machine) is going to hook, and I can move this up and down
a little bit, I can take this/get rid of it if you like. If this is in your way,
cut it out. It's really only there as a visual aid for vibration regulations in Europe.
So maybe you're in Europe and you're watching this. Cool, great! But if you're here in the
U.S. and you're watching this, this is irrelevant. It can come out so I have a little bit more play,
and then I also have the ability to move this handle. A lot of this
is being comfortable for me. What's my height? How tall or how short? What's going to feel
comfortable? I'm going to be out there for a half an hour or more. Let's make it work for you.
Okay moving down, this has the Stihl AutoCut 25-2. I'm not going to get into this in this video
but we have a great video on how to rewind this head so check it out/refer back to that.
It's going to help you avoid a lot of the problems that people have with a bump head
and not getting them to feed right. We do have a little bit of maintenance right here: this,
which is either going to use a 13 mm (1/2 in. if you don't have a 13 mm, that'll work)
and this little screw comes out. You can also use your T27 Torx that came with it,
and I have this tube of grease from Stihl. It is called SuperLube, and I'm simply
50 hours or so. For a lot of people once a year again: routines. I'm going to screw this in and
I'm going to give it a light squeeze, and I'm going to spin this head a couple times.
That's it, that's all I need. Just a little bit every year. If you do it, you're going to get
long life. You're talking probably never having a gearbox failure. If you fail to do it,
I see usually somewhere between 400-600 hundred hours depending on the application that a
gearbox is gonna fail, and it's dead. Not the end of the world; you can buy a new gearbox. But
if I can avoid that expense, I might as well. On this end, because I have a Stihl FS 91 that
is a shaft driven machine, I have a lot of options on what I can run on the end
of this. I can run the bump head, I can run a DuroCut 25-2 head that takes the strips of line,
I can run a PolyCut head, I can also purchase this blade installation kit/blade conversion kit
right here. This is going to have the larger deflector/larger guard. I know that's not
the proper term but the larger deflector and the hardware needed to mount a blade. It also is going
to have a little handle in there (or barrier bar as as it's called) that goes right here
that reduces the opportunity of this machine to kick back and the operator come in contact with
something spinning that's a little dangerous. So we've got a video on installing a blade,
that's also a great video. When you put a blade on these things it just makes it a completely
new machine. I mean let me tell you, around the yard, around the lawn, cutting grass..line
head. That's the way to go all day long. But as I'm getting out into some nastier, burlier stuff,
some heavier stuff...check out a blade kit. It is going to make this FS 91 shine. What else
do we need to know about it? We've covered all of the the basics on the maintenance,
we've covered how to start it, some of the things you can do with it, how to move some stuff around.
I'm a big fan of this Stil trimmer. The FS 91 has been been around for years, previously was
called the FS 90. It was refreshed a few years ago, giving it some some nice features like the
stop button and the choke that's connected to the throttle trigger and a better air filter
and a bigger fuel tank. You're gonna love this machine if you take the proper steps to
maintain it/to care for it when it comes to your fuel, when it comes to greasing your gearbox,
when it comes to maintaining your air filter. Let's have a long life with this machine so
that you can get the most out of it. Don't forget you can always refer back to your owner's manual
that you got when you bought it. The Stihl FS 91; it's going to give you the service scheduler, some
of the safety points, you also hopefully picked up this trimmer and brush cutter safety manual.
Not a bad idea to review that. These things are powerful, they can fling some stuff, so you always
want to be aware of what's going on around you and what you're trimming. Thanks for watching, thanks
for supporting Carl's Mower & Saw and your local Stihl dealer, helping you get the right equipment
to maintain your property, to make it pop, to make it beautiful, and the best place on the block!
Hey, this is Josh from Carl's Mower & Saw. Thanks for watching our videos! We're proud
of the fact that we've serving you with the best in outdoor power equipment since 1990.
We're glad that you had an opportunity to sit down and watch our videos, learn something about an
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