My trimmer has no power and struggles even under a small load. Also it does not want to rev up even with WOT. After about a minute of basically sitting there and idling at WOT it picks up and runs faster but the minute you apply a load it drops down again. Now here is what I checked so far. Spark plug is good and properly gaped. Valves operate as they should and lash is correct. Air intake filter and exhaust spark arrestor have been removed for testing, but both are clean. Any idea what the problem could be?
FS111R is sluggish
- Thread starter ueww40
- Start date
Tiger Small Engine
Well-Known Member
- Joined
- Dec 7, 2022
- Threads
- 2
- Messages
- 990
Sounds like partially dirty carburetor, or low compression. How old is it? Have you checked the condition of piston, rings, and cylinder visually?
DOM is June 2019. It starts right up on first pull but is kinda lazy to rev up. No I have not done any further checking on cylinder walls, rings etc. For that, I need to practically dismantle the engine and I am not at that point yet. I was hoping it was something easier like plugged up muffler (what are the odds of that?). Maybe it is a carburetor adjustment or cleaning problem or how about a timing problem?
Looks like the problem has been resolved. Turns out it was a carburetor problem of some sort. I almost gave up and was going to take the trimmer to Stihl and let them figure out what the problem is. Then I remembered that I had a small bottle of Mechanic in a Bottle sitting on my shelf and I said to myself, give it a shot before you take it to Stihl. I put a tablespoon of this stuff in the gas tank and started the trimmer and it was limping along just like it did before, but all of a sudden after about 5 minutes or so it showed signs of running a little faster and the rest is history. After doing about an hour's worth of trimming by the end of that time my trimmer was running like a bat straight out of hell. Frankly I couldn't believe it. That potion actually did what the bottle said it would do, clean up everything inside, dissolve gum, soften flapper valves etc., etc. I will check it again in a couple of days, but I am pretty sure now a dirty carburetor was the problem. That wonder potion is still in the carburetor now and working. Thanks for hinting on the carburetor. You guys were right.
I don't know about the FS-111R, but I had a pole saw with a similar powerhead on it, think it was an HT-131 maybe. I went to tune the machine for resale, and it just didn't seem to want to tune, seemed sluggish to rev up, didn't seem to run WOT like I thought it should either, much of what you're describing above.
So, I went to the computer and started searching for "issues" related to the running of that powerhead. As it turns out, that model is one of Stihl's "4-Mix" models. That means that it's a 4-stroke engine, but it uses 2-stroke oil/fuel mix to lubricate the engine. What does that mean performance-wise?
It's going to not have that high-strung sound like a 2-stroke, and it's not going to "tune" to 10,000rpm, 11,000rpm, etc. If I recall correctly, it tunes to WOT at about 7500rpm. And that is what I was seeing trying to "tune" my HT-131 BEFORE I realized it's a 4-stroke engine.
By the time I got to this paragraph, I looked up the FS-111R, and it IS a Stihl 4-Mix motor. So, you've got a 4-stroke engine that uses a 2-cycle oil/fuel mix. It's not going to rev like a 2-stroke, so it's not going to sound like 2-stroke (it's a 4-stroke). It will have LOTS of torque and power and will still cut like a 2-stroke at full throttle. Mid-range is a little "iffy"...
Hope that helps! Here's a few links worth watching:
Here's a good description of the 4-Mix motor:
Here's a guy that uses trimmers all day long and his take on the 2-strokes versus the 4-mixes: