Stihl FS 90 - Holy CR@&!!

trouty(z5)October 7, 2006

So I went out today and picked up a Stihl FS 90 from my local dealer. I've been looking around for a replacement for my cheap HD John Deere trimmer. Walked in the door and the FS 90 was on sale for $50 off. Didn't even hesitate.

Got it home, fired it up and wow what a difference! It has what Stihl calls a 4-mix engine. It's still a two stroke, but supposedly has more power and torque. All I know is that it ran much more smoothly than the Deere (Homelite, I think), and handled the same stuff with less effort. Solid driveshaft and will handle a number of accessories.

One thing the rep told me was to be sure to use 89 octane gas.

Good purchase.

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canguy(British Columbia)

The FS90 is a 28cc version of the 4-mix that is replacing the 85 series two stroke. It is a 4 stroke with valves like the FS110 but is smaller and lighter. As trouty has discovered, torque is phenominal. Install .105 line in the quick load head and hit the weeds. Carumba!!

    Bookmark   October 7, 2006 at 11:03PM
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newjerseybt(5b NE PA)

I noticed that all the string trimmers are on sale except the "saw" models.

Too bad the chain saws aren't on sale.

I am going to replace my Homelite with the FS90 model which has the bicycle handles and the flexible straight shaft which might have an advantage for straight edging.

My dad likes his Homelite but his curved shaft model has starting problems. I'll give him my straight shaft HomeLite which runs good and go for the gold.

I was going to consider an Echo but with the discount....Stihl wins.

    Bookmark   October 8, 2006 at 10:55AM
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Actually canguy it is a 2 stroke - uses 50:1 mix. But it sure feels like a four.

    Bookmark   October 8, 2006 at 9:15PM
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Oil in the fuel has nothing to do with whether it is a 2 stroke. IT IS A 4 STROKE ENGINE!!! Do you think if you dump 2 stroke oil in your car you are driving a 2 stroke car? The reason the 4 mix uses oil in the mix is because it does not have an oil sump, and uses oil in the fuel to lubricate the crankcase. This allows it to operate in any position. However, THERE IS ONE POWER STROKE PER FOUR STROKES OF ENGINE ROTATION.

    Bookmark   October 8, 2006 at 11:35PM
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Thanks, I learned a new thing!

    Bookmark   October 9, 2006 at 12:08AM
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nevada_walrus(Boulder City)

Yep, that's why it is called a 4-Mix. It is a four stroke engine that uses 2 stroke mix oiling. Best of both worlds. Never has dirty oil but has the bottom grunt of a 4 stroke. Along with the cleaner emissions of a 4 stroke.

Just stay away from the back pack versions. For now. We have seen a number of problems with the larger 4-Mix used on back pack blowers but little to none on the smaller versions.

    Bookmark   October 9, 2006 at 9:05AM
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tdsjd(z5 MA)


What problems are you seeing with the larger 4-Mix engines. I have a BR600 backpack blower with a 4-Mix. Only about 30hrs on it so far, no problems yet.


    Bookmark   October 9, 2006 at 12:33PM
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canguy(British Columbia)

We have seen a small number of bearing failures and one camshaft go south. Stihl refused warranty on a couple because the operator was using Opti-2 and sent the dealers a letter warning about using oils other than theirs. Amsoil and Interlube both countered by saying that is nonsense and ask the dealers to submit any refused claims to them for evaluation.

    Bookmark   October 9, 2006 at 1:53PM
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newjerseybt(5b NE PA)

"Amsoil and Interlube both countered by saying that is nonsense and ask the dealers to submit any refused claims to them for evaluation."

Sounds like a potential lawsuit. Also makes one start to rethink their new OPE purchases.

    Bookmark   October 9, 2006 at 2:41PM
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tdsjd(z5 MA)

Would be intersting to hear how that one works out as I've been running Amsoil at 80:1 in my 4-mix and all my 2 strokes.

    Bookmark   October 9, 2006 at 11:05PM
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nevada_walrus(Boulder City)

heavy carbon build up in the combuston chamber causing valve failure and seal leaks causing a lean out condition. For some time even though they claimed not have ever seen these problems they warrantied them, even knew the short block number by memory. Go figure. Lately they have got real picky about doing warranty.

They are telling us that customers should be using their synthetic oil to prevent the carbon build up. My opinion is if the problem developes using their regular oil, something is serious wrong with the engine design used on the back packs.

For the most part these problems are happening after 100 to 200 hrs of use by commercial users. These same people got 500 to 1000 hrs out of their 2 stroke Stihl back pack blowers so its not the users.

These are great blowers, nice sound, blow more air then anything I can recall. They just need to fix the problem and quit the song and dance routine.

    Bookmark   October 9, 2006 at 11:32PM
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I need a new trimmer and this looks like a decent unit. How much did you pay?
Can these trimmers be used in any orientation? For example can I use the trimmer to edge my garden beds. I guess you will have to turn the unit on it's side.

    Bookmark   October 11, 2006 at 12:41PM
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canguy(British Columbia)

Treat it the same as a 2 stroke, it has a diaphragm carb and uses mixed gas. The only additional maintenance is checking the valve clearaances every 135 hours, easy on the trimmers but a little more involved on the blowers.

    Bookmark   October 11, 2006 at 3:26PM
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Hi scaly, I paid about $250, $50 off of the list of $299. And yes, you can use it as an edger.

    Bookmark   October 11, 2006 at 9:42PM
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Scaly, Nice thing about this thing is you can turn the head in any orientation and keep the power unint in the upright position (if you like) .

    Bookmark   October 12, 2006 at 9:53AM
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There is so much torque that I feel like I can do most of my trimming just above idle!

Another happy FS90 owner.

    Bookmark   October 31, 2006 at 10:43AM
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newjerseybt(5b NE PA)

You can add one more FS90 happy owner and a Phil Rizzuto "holy cow"!

What a difference from my Homelite!

Easy to start, no more constant reloading, quieter, smoother, cuts the heavy stuff with ease, also seems to burn cleaner. Good balance with the shoulder strap which is important when doing 1000 feet per week.

The "free" glasses are getting a workout. I got hit in the face a few times already. Maybe I am not using it at the best angle.

Unfortunately I only got to use it twice as the cold weather is setting in.

I highly recommend this trimmer.

    Bookmark   November 1, 2006 at 4:27PM
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I purchased the STIHL KM110R Power Head with the extended hedge trimmer this year. I only used it about 15 hours to trim my tall hedge. I used ECHO premium blended oil. The STIHL dealer said it would be OK to use it. They did not have the new STIHL Ultra full synthetic oil yet. What do you think of the reliability of this power head? It sure ran great. Easy to start, and plenty of power. I was thinking of getting the BR600 backpack next season. By then, their Ultra oil will be available. Do you think they will be able to fix the problems with the backpacks? I would think STIHL has a lot riding on this unit. They better make it right, or drop the 4mix engines and go back to the 2 stroke engines. Charles Ranheim

    Bookmark   November 1, 2006 at 10:53PM
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Hi folks,
I think this is what I need also. Do they have both string and blade (interchangeable)? Do they come with both new?
Are they tuff enough on brush (nothing major, just heavy weeds and briars)? Does anyone know of an online source for info (capabilities) of a specific model, that would help a guy decide which one to buy? I'm stationed in Germany (Stihl land) but the prices on them here are outrageous. The FS90 sells for 450 Euro at the local dealer ($1 buys .76 Euro). I do the research and pick out something, then have my buddy buy it and mail it to me.
The main thing I want it for is to clean up in and around several pastures that I have. I have a weedeater gas string trimmer that does OK, and I just bought an offbrand backpack model that I can't stand. The folks that clean up the roads etc have Stihl everything and hardly work up a sweat running them. Should I think about something bigger?


    Bookmark   November 4, 2006 at 8:56PM
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canguy(British Columbia)

They have strong torque which is great for brushcutting, line heads and blades are readly available.The 4-mix backpacks offer a lot more power with little additional weight.

    Bookmark   November 4, 2006 at 11:38PM
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nevada_walrus(Boulder City)

Crabheim the smaller trimmer 4-Mix came out a couple of years ahead of the back pack blower. We have seen no increase in trouble frequency over similar 2 strokes. Your use of Echo oil should be no problem, shouldn't be in the back pack either but when the Stihl synthetic becomes available it may be a good idea to use it anyway.

Dropping the 4-Mix or some version of small 4 stroke may not be a realiatic option. I personally believe that 2 strokes are a zombie, walking dead. I do not believe they will survive coming increased emission requirements. Include in the emission requirements that of noise. The annoying whine of the 2 stroke is finding more and more cities, homeowners associations and counties restricting or even banning their use. The small 4 strokes don't have that problem.

    Bookmark   November 5, 2006 at 12:49AM
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canguy(British Columbia)

LOL. I have to admit I still like two strokes for their simplicity and high power to weight (and the cool burble at idle)but the new mini 4 strokes do have a number of advantages. Maybe I am just a dinosaur too.

    Bookmark   November 5, 2006 at 12:00PM
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Am I the only one who thinks that the engine feels like it could easily spin a longer length of line than the factory shield will allow?

    Bookmark   November 13, 2006 at 2:01PM
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newjerseybt(5b NE PA)


I just took out the FS-90 for another look. The head on the Stihl is much greater in diameter than the Homelite that I had. The Homelite had a bit more line reach.


After RESTRINGING the head, the Homelite had a tendency to "fold into itself" and wrap the line around the shaft especially if you were just 2 inches too long beyond the shield cutter. That never happens with the Stihl.

For the average homeowner, that was just a little annoyance, but for a professional landscaper, a problem like that is more serious.

It is possible that you can go 1 more inch on the line length though and I know what you are talking about.

    Bookmark   November 14, 2006 at 9:16AM
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canguy(British Columbia)

The engine might pull it but it won't cut as well because the line will whip excessively. Don't take the guard off, it is there for your protection. Some of our lawn care contractors do it but if anyone gets hurt, look out.

    Bookmark   November 14, 2006 at 10:30AM
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I found another effective use for the FS90 last weekend. I need to bag my leaves for collection at the curb. After blowing the leaves into piles, I chopped/reduced them with the FS90 a bit before bagging. I used fewer bags and the chopped up leaves are easier to fill than the fluffy whole leaves.

    Bookmark   November 23, 2006 at 12:03AM
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masiman(z7 VA)

I put on the brush blade and dunk mine into my leaf compost bin. 10 minutes of that and it is good to go. Not as fine as a leaf shredder nor do I get it all, but I don't have spend $1000+ for a decent chipper/shredder.

    Bookmark   November 23, 2006 at 1:56PM
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I bought my Stihl at a dealership. The salesman pointed out these units are not "throw aways," so I spent more than $300 rather than less than $100. ("Throw aways" are small, light wackers that cost more to repair than they are worth, so if they break you "throw them away.") I think I made the right decision buy I�m not sure. My old wacker was electric powered and dragging the cord was a pain. Gas power is more convenient.
I have owned my unit for over a year and run it a dozen times. It doesn�t get mistreated or overused at our vacation home. I like its power and brand name backing. It is reliable and sturdy. But there are some irritating faults.
Starting is always a problem. It never starts after priming on less than ten pulls. I always have to switch the switch from "cold" to "hot." Then it catches. I think this can and should be improved. My Craftsman power mower ALWAYS starts on the first pull every time. Why can�t the wacker do this?
My biggest gripe is the full cap. That�s because it�s a pure safety issue and very dangerous. Sealing the cap is clunky, difficult and a very poor design. If you do not fit the cap precisely and exactly, it will not seal. I have limited storage so I used to gently stand the unit on the motor, upright. The last time I put it away I smelled gasoline. Checking around the unit I discovered the gas cap had been unseated and leaked gasoline on the floor. Yes, it was my fault I hadn�t exactly seated the cap and yes, I should have checked it more carefully. But Stihl should design a better cap that fits as tightly and is easier to seal.
Another major problem is the throttle. It�s hand controlled under the stem. Perhaps there�s no other way. Still, it�s a hair trigger, meaning there is no good way to manage RPM or power; it�s either running too fast or not fast enough. At first I thought I would get better with experience and be more efficient. Can�t be done. Bad design.
One gets used to the weight over time. I bought a sling to carry the unit and carefully balanced the unit so it sits comfortably. This is essential because the unit isn�t very light.
Another hassle is restringing the whip. I asked the dealer for a demo and he told me to go on to Stihl�s website for a tutorial. Directions are NOT in the manual. Why is this so impractical?
Mixing gas and oil is not troublesome or expensive. The salesman said the 50 to 1 gas to oil dilution would not hurt my mower, so it in both engines.

    Bookmark   July 2, 2011 at 11:32AM
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