Getting more zip out of a Stihl FS-131

[Farmchuck]

Hello. I recently purchased a new Stihl FS-131 bike handle trimmer. It sounds like it’s turning SO much slower than my FS-80 of my Husqvarna 525. Any way to remedy this? Looks like there are plastic caps of some sort on the carb adjustment screws. I read somewhere about removing the spark screen from the muffler might help. I don’t typically mess around with stuff much so I’m not super familiar. Any suggestions would be appreciated. Thanks guys.

 

[emanuel]

Check the air filter first, make sure its not stuffed up with crud. Same with the muffler, make sure you clean the spark arrestor. In the end the engine is an air pump, without free airflow in and out, any kind of fuel/air mixture tuning wont bring you the desired results. Once that is done, if the issue persists, you can try a slight carb tune, and hopefully there’s no other hidden issues besides this. Make sure the fuel mix is fresh btw

 

[Farmchuck]

Check the air filter first, make sure its not stuffed up with crud. Same with the muffler, make sure you clean the spark arrestor. In the end the engine is an air pump, without free airflow in and out, any kind of fuel/air mixture tuning wont bring you the desired results. Once that is done, if the issue persists, you can try a slight carb tune, and hopefully there’s no other hidden issues besides this. Make sure the fuel mix is fresh btw

Thank you for the information. The trimmer is new and only on its 5th tank of gas. I am using canned VP fuel so i think thats okay. I'm not really sure how to tune the carb with those plastic caps on the screws. Thanks again.

 

[Brad Button]

There is a BIG difference between the fs 131 and fs 80. The fs 80 is a 2 stroke which runs at a LOT higher rpm. The fs 131 is a 4-mix, 4-stroke engine with a much lower rpm but more torque. Where the 2-stroke would start to bog under a load the 4 mix will not. There is no way that I have ever seen to increase your rpm on that type of engine.

 

[EFSM]

The coils have a rev limiter, so there is only so much you can do.

 

[Farmchuck]

Thank you for the replies. I guess I’ve just been running the FS 80 so long I’m used to the sound. This FS 131. Sounds like a dog compared to it. I guess I’ll just have to get used to it.

 

[Bill G]

Hello. I recently purchased a new Stihl FS-131 bike handle trimmer. It sounds like it’s turning SO much slower than my FS-80 of my Husqvarna 525. Any way to remedy this? Looks like there are plastic caps of some sort on the carb adjustment screws. I read somewhere about removing the spark screen from the muffler might help. I don’t typically mess around with stuff much so I’m not super familiar. Any suggestions would be appreciated. Thanks guys.

Here was a few days ago.........

I just installed a new Stihl 30-2 Durocher head on a new Fa-131 bike handle trimmer I picked up on Monday. I put some .120 Stihl CF3 Pro pre cut pieces of line on it & it is definitely cutting much better than my FS-80 with .105 line. I’ve cutting some pretty heavy green vegetation with no problem at all. I have not gotten into anything dry or woody yet so I don’t know how it will handle that. I’m having trouble getting used to this trimmer. 3 tanks of fuel & it’s not really waking up yet. It cuts well but sounds like a LOT less RPMs than the FS-80. Wonder if there are any mods for it to wake it up a bit. Someone suggested removing the spark arrestor from the muffler. Not really sure if that would help or not.

The reason you notice the RPM difference is the FS80 is a true 2 stroke and the FS131 is a 4 mix.

 

[Woodpecker]

Thank you for the replies. I guess I’ve just been running the FS 80 so long I’m used to the sound. This FS 131. Sounds like a dog compared to it. I guess I’ll just have to get used to it.

Basically the same answer you got over on FHC.

It’s a 4 stroke engine. It will run right through stuff that would bog down a 2 stroke trimmer. Great for brush heads. Some prefer a 2 stroke trimmer for running trimmer line because of the supposedly faster line speed. I’ve never noticed a difference in trimmer line speed of 2stroke vs. 4 stroke. The 131 is just able to tractor through tougher stuff than a 2 stroke. It’s a tank! I’d recommend removing the guard and running your line at 12” with that power head like the pros do. That could be a little harder on the head but I doubt you’ll ever hurt it in a residential type scenario.

 

[Farmchuck]

Thanks fellas. I’ve read a few responses & I’m getting the it has more torque part. I’m just not understanding when people say 4 mix or 4 stroke. When I hear that I think of a lawnmower or something. I also think Bill G should give that Stihl 20-2 head a try. I don’t think he’ll be disappointed.

 

[bogieboy]

Basically the same answer you got over on FHC.

It’s a 4 stroke engine. It will run right through stuff that would bog down a 2 stroke trimmer. Great for brush heads. Some prefer a 2 stroke trimmer for running trimmer line because of the supposedly faster line speed. I’ve never noticed a difference in trimmer line speed of 2stroke vs. 4 stroke. The 131 is just able to tractor through tougher stuff than a 2 stroke. It’s a tank! I’d recommend removing the guard and running your line at 12” with that power head like the pros do. That could be a little harder on the head but I doubt you’ll ever hurt it in a residential type scenario.

There isnt a line speed difference on stihl.... the 4 mix trimmers have a higher gear ratio in the gear head, to compensate for the 11,5k limiter....

@Farmchuck the reason its called a 4 mix or 4 stroke, it has valves, and operates like a lawn mower engine, its a 4 stroke motor, which is lubricated by the oil in the fuel, which is allowed to run thru the whole crankcase due to the engine design, part of the intake tract, before thw intake valve, opens up into the crankcase to allow lubrication, instead of your fs80 which is a 2 stroke, specifically piston port timing 2 stroke. They will sound completely different to one another, i personnally prefer the sound of the 4 mix motors, being the owner of an older fs130 myself... only trimmer that had more balls than the 130/131 that i have run was an old fs250 with an unlimited rpm coil...that thing ripped thru everything in its way....

 

[Farmchuck]

Could you put an unlimited coil on the131 or because its a 4 mix/4 stroke it would't work the same?

 

[Bill G]

...only trimmer that had more balls than the 130/131 that i have run was an old fs250 with an unlimited rpm coil...that thing ripped thru everything in its way....

Try one of these

 

[Farmchuck]

Try one of theseView attachment 422900View attachment 422901

I'll bet that things a beast!

 

[bogieboy]

Could you put an unlimited coil on the131 or because its a 4 mix/4 stroke it would't work the same?

No.... you dont want to spin the 4 mix motors any faster, as you will run into all the issues of pushrod valvetrain design, valve float, loss of power, destruction...LOL also, you dont want to spin the plastic cam any faster as it can and will melt....

 

[Farmchuck]

No.... you dont want to spin the 4 mix motors any faster, as you will run into all the issues of pushrod valvetrain design, valve float, loss of power, destruction...LOL also, you dont want to spin the plastic cam any faster as it can and will melt....

Yikes! Nope I guess that wouldn’t be a very good idea. Thank for the information in your posts. Greatly appreciated.

 

[docsimon520]

I bought a 131 for the wife; I have a 240 2 stroke. Was annoyed when I realized it was a four stroke on the 131 and it just looked like it wasn’t doing the job that the 240 does however I put some .105 echo black diamond on it and that thing just tears the *s-word out of 3 foot tall grass. I went out and bought a 131 for myself and am perfectly happy with it. It does sound like it runs half the speed of the 240 but where the 240 bogs down, the 131 just powers through. Very impressive and able to clear our dam and low lying areas well. I haven’t run the 240 since I bought the 131.

 

[Farmchuck]

That was exactly my experience. It sounds like it’s only running at half throttle but it does seem to have the power. I’ve never tried Echo black diamond line. I’ll have to get my hands on some.

 

[BromFS250]

Thanks fellas. I’ve read a few responses & I’m getting the it has more torque part. I’m just not understanding when people say 4 mix or 4 stroke. When I hear that I think of a lawnmower or something. I also think Bill G should give that Stihl 20-2 head a try. I don’t think he’ll be disappointed.

That 20 -2 head is awesome if you put some of the bigger braided line in it... It comes with a few strands of some line that I destroyed easily. But I love the way it cuts, on the down side you have to change out strands a lot. Until they come out with indestructible line. Right?...

 

[Mycamaro_68]

That was exactly my experience. It sounds like it’s only running at half throttle but it does seem to have the power. I’ve never tried Echo black diamond line. I’ll have to get my hands on some.

I have never messed with a Stihl 4mix before but my understanding of typical 4 stroke is the reason it sounds like it is running half the speed is because at the same rpm the 4 stroke has half as many ignition events. A 2 stroke fires ignition every revolution where as the 4 stroke fires ignition every other rotation.

 

[Moparmyway]

I have never messed with a Stihl 4mix before but my understanding of typical 4 stroke is the reason it sounds like it is running half the speed is because at the same rpm the 4 stroke has half as many ignition events. A 2 stroke fires ignition every revolution where as the 4 stroke fires ignition every other rotation.

Still can’t overcome the rpm disparity.

Most 4 stroke lawnmowers, snowblowers, etc. run between 3000-3500 rpm

Most chainsaws are running up to 4x that