Stihl FS40C String Trimmer First Use and Review

Reader Contribution by Allan Douglas
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I recently wrote about my adventure in trimmer shopping, this is the follow-up to that piece as a review of my new Stihl FS40C string trimmer.

Stumbling Start

Testing was delayed by the fact that I didn’t have a 1-gallon gas can. I have several 2-gallon cans, and one is a can into which I pump precisely 2 gallons of gas for use in my 2-stroke equipment. I have some gas/oil mixed up but that’s a 40:1 mix for my older tools. The Stihl FS40C string trimmer uses a 50:1 mix.

I bought a six-pack of synthetic oil for the Stihl, each bottle mixes with one gallon of gasoline. I figured I’d use that can of new gas and two bottles of oil and be all set to fire up and see what it can do. But the manual and some commentary online talk about the need to use the gas/synthetic oil mix within 30 days or it begins to decompose, and using degraded gas/oil can void the extended warranty (four years) Stihl offers. In fact, in reading the warranty there are several ways they try to get out of paying for repairs during that second two-year period.

So I popped down to the closest hardware store and bought a 1-gallon gas can, mixed in the Stihl oil, and filled the trimmer’s gas tank.

Firing Up My Stihl FS40C String Trimmer

The controls and start-up procedure are standard and familiar. This does have a convenient feature that opens the choke automatically if I gun the engine a little after start-up.

I pushed the primer bulb five times and the trimmer started up on the third pull. It would probably have started on the first or second had I primed it more. The first two presses on the bulb passed nothing but air — being brand new and never run.

One of the issues I’ve had with my old trimmer was keeping it running while at idle. It tended to die if I didn’t gun the throttle a little while walking from one spot to the next. If I had to set it down to open a gate it was sure to quit on me; but it started up again, so it was no big deal.


As you can see, I could set this one down and leave it for a long time and it continues to purr right along.

Gas Mileage

One of the few complaints I saw in reviews on the Stihl FS40C string trimmer was that it has a small fuel tank and requires frequent fill-ups. But I found this not to be the case. Maybe it was an old review and the issue has been addressed since, or maybe the reviewer expects to trim for three hours solid. I trimmed my workshop yard (small but steep) and the dog’s play yard (1/3 acre) and still had some fuel left in the tank. That’s plenty of “mileage” for me in one session.

Power and Performance

At 27cc this engine is a bit smaller than the 31cc in my Poulon, but the Stihl FS40C string trimmer had no trouble powering through grass and standing weeds. The .80 line it uses punched through the small brushy stuff better than the .65 line on my Poulon. The bump feed on the line is not as touchy as the old one had gotten to be, either. I tended to use up line faster than I should because accidental bumps against the ground would feed line that just got cut off by the blade.  Not a problem with the new Stihl.

As I was working, I did notice that the engine went “flat” a few times. Each time I told myself, “OK, here we are running out of gas already,” but then it picked up power and kept going.  I’m not sure what that was about.

The throttle is responsive, the engine not too loud, and the unit is lighter in weight than my old one. This is largely because of the shaft design I chose.

Which Shaft?

You have three choices to make in trimmer shafts:

  • straight shaft or curved
  • long shaft or short
  • split shaft or solid

Curved or Straight?

Straight shafts use a mechanical gearbox on the end of the shaft to change the direction of power and channel it into the cutter head. Curved shafts use a flexible cable inside a housing to transmit power to the cutting head.

A straight shaft offers a lower cutting head, thereby being better at getting underneath fence rails, sheds, shrubbery, and so forth. The gear box makes the end of the shaft heavier, but is said to be more efficient in transmitting power to the cutting head. Just make sure you check the oil in the gear box occasionally.

The curved shaft eliminates that cast metal housing and gears, thereby making the shaft lighter. The trade-off is that the cable running through a curved shaft can create friction, and some folks complain about frequent failure of these cables. Mostly in low-end brands, though. I’d expect Stihl to use a properly sealed and lubricated cable and housing. I saw no complaints about this in product reviews by other buyers.

Long or Short?

Both styles come in a long-shaft and a short-shaft version. If you need a long reach (like reaching over a brow to cut a steep embankment) a long shaft is handy.  For tight quarters the short shaft is great.

Split or Solid?

Both styles also offer a split-shaft version that allows you to change out the implement on the end of the shaft. String trimmer, brush cutter, pole saw, leaf blower, edger, and cultivator are some of the attachments available for some of these systems.

I had the cultivator (tiller) and the brush cutter blade for my Poulon, but rarely used them. I decided to forgo the split-shaft this time around. I also bought a curved shaft for the first time, and a short shaft at that.

Putting It To Work

I noticed the difference right off. Not having the long shaft with gear box cantilevered out on the end of it made the trimmer much easier to handle. It felt weird having the cutter so close to my feet, though. I will definitely miss that long shaft when weed-whacking up in Copperhead County. That extra few feet of exploratory distance was comforting.

But working around my walkways and lumber piles was much easier because I wasn’t doing so much jockeying to move through the tight spaces and get into the corners.

In order to get the cutter head parallel to the ground, I still had to hike the engine up my side, but that’s because I’m short. The short shaft did help a bit as the hot engine did not have to be tucked up into my armpit.

Stihl FS40C String Trimmer Conclusion

I’ve used this string trimmer several times now and have found it to start right up, run strong (those momentary power drops have not repeated), and have plenty of power and work time. The lighter weight makes trimming less of a chore, too. I’m happy.

More Info: Listing on Stihl web site

  • Published on Aug 23, 2017
Tagged with: Reader Contributions
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