stihl trimmer no power?

[The motor guy]

So I bought a new fs100rx string trimmer a couple weeks ago. I was expecting this thing to be even more of a beast compared to my echo trimmer, but it really doesn't have much more power than my smaller sized srm-225 echo. I also have an srm-266 which I can let like 2ft of line out and it will spin it with only needing about 1/3rd of the throttle, so I'm not sure what's going on. I find it seems to run lean when it gets down to about 1/2 a tank and also when it's good and hot the engine loses power

 

[Avery4]

Take it back and ask for a repair, refund or replacement. That is an expensive tool, and should run properly.

 

[The motor guy]

I'm mainly curious as to what you guys think? I'd like to see if I can tune the carb better, I just want to know if my description describes a lean running engine. Does running lean cause a loss of power? I thought racers always ran lean because it created more power.

 

[The motor guy]

Well the problem is if I put the guard back on and take it to the dealer it will probably be fine, because of course the guard doesn't let out much string, so it has plenty of power to spin that, The other issue is it takes about 10 minutes for the problem to arise, so they will just look at me like I'm freaking crazy and say nothing is wrong.

 

[Fsharp]

So when you take the guard off and run two feet of line the engine overheats and loses power lol. I'm with the dealer on this one.

Good luck trying to adjust that carburetor, I doubt you can change anything on it but idle speed.

 

[Andrew1972]

You are business not a tinkerer. Return or have the tool fix the new tool and make money.

These expensive tools are your livelihood.

 

[freshcopedawg]

Take it back and get the 130.

 

[The motor guy]

Originally Posted By: Fsharp
So when you take the guard off and run two feet of line the engine overheats and loses power lol. I'm with the dealer on this one.

Good luck trying to adjust that carburetor, I doubt you can change anything on it but idle speed.



No it has hi and low speed jets. That's just it the engine doesn't have the power to run two feet of line. You have to listen to the engine, The echo runs can run several inches out past the guard with no problem and no engine overloading, the stihl I can maybe run an extra inch or so, after that the engine is at it's limit. People always say you'll burn out the clutch, I've never burned one out, but I also don't overload the engine like many guys do.

 

[The motor guy]

I'll just put it on craigslist and knock $25 bucks off the price. Someone will buy it. There isn't anything wrong with this machine it just doesn't have the power I need. It feels like I'm cutting with a pair of scissors with this thing. It's been driving me nuts all week.

 

[BigD1]

Check that spark arrester, and give it a good cleaning if it needs it.

 

[Merkava_4]

Originally Posted By: motor_oil_madman
Does running lean cause a loss of power?


Yes and so does running too rich. The engine produces the most power when the fuel/air mixture ratio is correct for the atmospheric location you're at.

 

[The motor guy]

I see. I think this is the third piece of equipment I've bought that I've had to adjust because of this. I think these things come from way up north or somewhere where elevation is higher then they send them down to 10ft above sea level and they run borderline lean. Not enough for the people at the dealer to notice before they sell it, but noticeable once they run in a bit. I had a blower that ran great then once I had about 50hrs on it the blower would bog down if you went past 90 percent full throttle. It was running lean and just needed a carb adjustment. I'm pretty sure this one is running lean too, but since I'm not used to how the four strokes sound compared to the 2 strokes, it took a while to develop an ear for what it was doing. Thanks. I'll tinker with the adjustment screws and see. I bet just richening up the low speed screw will fix it.

 

[The motor guy]

Originally Posted By: BigD1
Check that spark arrester, and give it a good cleaning if it needs it.


It's ok. They actually put the spark arrestor on the exhaust opening where you can see it instead of being hidden behind a deflector of some sort.

 

[Merkava_4]

Originally Posted By: motor_oil_madman
I'll tinker with the adjustment screws and see.


It's easy to set mixture. All you do is adjust the idle mixture screw to get the highest RPM idle speed between full lean and full rich. The RPM will drop off when either going too lean or too rich. The same method applies to the high speed mixtures screw. Pull the trigger all the way and get the highest speed between full lean and full rich. After that's dialed in, you can richen it slightly if it bogs down under load.

 

[The motor guy]

Ok. So I got the low speed set so it's as responsive as possible with no bogging. Now my question for the hi speed is that I don't want to lean it out too much and mess up the engine. So I ran it at full throttle and I turned it out until the saw started losing rpm and then I turned it back in about 1/4 turn. So pulling it out was making it run rich, but can I go the other way and lean it out until it starts to lose rpm and then back off 1/2 a turn or so? I just don't want to set it too lean.

 

[Merkava_4]

Originally Posted By: motor_oil_madman
So pulling it out was making it run rich, but can I go the other way and lean it out until it starts to lose rpm and then back off 1/2 a turn or so?


Yes, full lean and full rich are the drop-off points. As you're turning the screw to the right leaning it out - and you start to hear the engine slow down - turn the screw back to the left until you hear the engine speed up. When the engine has its mixture set correctly, it makes more power and speeds up.

 

[The motor guy]

Ok, so I'm not going to hurt anything leaning it out until it slows down a bit and then finding the middle? I just don't want to burn a piston or something.

 

[The motor guy]

It was running a bit lean on the low speed side, but it's still using a ton of fuel. It burned through the whole tank just about when I was tuning it and I don't think I spent more than 20 minutes tinkering with it.

 

[Merkava_4]

Originally Posted By: motor_oil_madman
Ok, so I'm not going to hurt anything leaning it out until it slows down a bit and then finding the middle? I just don't want to burn a piston or something.


Yes, you're looking for the sweet spot:

1. Full lean it slows down
2. In the middle it speeds up
3. Full rich it slows down again

 

[The motor guy]

Ok, so maybe it was running a bit rich on the high side. which would explain the fuel usage. It was running lean on the low side because I opened the jet about a quarter turn and it made the throttle response off idle nice a snappy. It's been a while since I've adjusted a carb, but if I remember right their is usually about one full turn in between lean and rich on this little carbs. I'm just a little paranoid on making sure I do it right since this machine is brand new. I'll tinker with it tomorrow and see if I can get it closer to the sweet spot on the hi speed side. Thanks. Right now I have the throttle response off idle about the same as a 2 stroke with very little lag and it also seems to run at low speed a lot smoother too. I'm still on the fence about keeping this machine because it's still pretty underpowered compared to what I'm used to. It's always better to have more power than necessary, because they slowly lose power over time.