trimmer loses power when hot

[The motor guy]

I can't really tell if this machine is running rich or lean, because it doesn't change tone like a 2 stroke does. A 2 stroke will run smooth and have that screaming tone to it when set lean. The only thing I notice is it's a little hard to keep at a steady rpm, it kind of wants to rev up and down a little even though I'm not moving the throttle. This is a stihl 4 mix trimmer and supposedly the factory settings are 2.25 turns on the hi side and .75 on the low side. The funny thing is I can shut it off and restart it and it will have good power for 10 seconds and then lose it. Before I figured out what the factory setting was I leaned out the hi speed screw until the trimmer lost rpm and then backed off until it ran the highest and then I backed off about 3/4 or a turn past that, which put it at like 1.75 turns out and I didn't have any power loss issues and I was happy with the trimmer, so I don't know. What do you guys think? Should I just put it back to the way I had it before? I'm about to give up on this thing, also the idle speed keeps coming out of adjustment and drops after a week of use.

 

[Trav]

Get it set right then put just a drop of 290 on the screw threads, you do not need to remove the screw it wicks in and will hold them tight, don't get carried away a drop is all it needs. This is a bigger bottle but you can get small ones.

https://www.amazon.com/Loctite-37481-Penetrating-Threadlocker-36-milliliter/dp/B0002KKTRM

 

[The motor guy]

What do you think causes it to lose power?

 

[Fsharp]

Sounds like it's lean but you said it works best at 1.75 turns instead of 2.25 turns. I'm assuming that these are turns OUT so it's leaner than why you said it works best at.

That being said... If it has a choke, try choking it a little and if it runs better than it's too lean.

 

[The motor guy]

Originally Posted By: Fsharp
Sounds like it's lean but you said it works best at 1.75 turns instead of 2.25 turns. I'm assuming that these are turns OUT so it's leaner than why you said it works best at.

That being said... If it has a choke, try choking it a little and if it runs better than it's too lean.


I tried that, didn't really notice anything, it's kind of hard to tell because it's either full choke or no choke and hard to hold it between the two.

 

[The motor guy]

I noticed that from idle to 90 percent throttle it has clear exhaust, but from 90-100 it puts out a slight haze of smoke, so I would assume that it's running a bit rich? It clears up after 10 seconds of full throttle though.

 

[silveravant]

Have you checked the spark arrester/muffler?

 

[dave123]

Isn't this machine new if under warranty let dealer mess with it.

 

[The motor guy]

Originally Posted By: dave123
Isn't this machine new if under warranty let dealer mess with it.


Yeah, but I always run with the guard off on my trimmers and I doubt it will do it with the guard on since it doesn't let line out. I suppose I could bring it to them with it off and if they say no warranty, oh well I'll sell it.

Please keep in mind I'm not one of those idiots who overloads their trimmer by letting too much line out. I only let a little bit more than what it would have with the guard on. Like 2" more on each side. I also have an echo srm-225 which is echos bottom of the line 21.2cc engine and it only lets out about as much line as that thing can handle with no guard. This stihl is a 31.4cc engine.

 

[dave123]

Well if it run with guard on and run properly but with guard off and extra line out meaning more load on motor hmm sounds like it isn't the engine but operator error what size line???

 

[zzyzzx]

Throw it away and get an electric one.

 

[ironman_gq]

I'm pretty sure that thing uses a rev limited coil which makes tuning by ear kinda tricky.

 

[bmwpowere36m3]

Which model Stihl?

I have a FS-90R and it runs great... first couple tanks at 40:1 with Stihl Ultra and 89 E10 and now 50:1. My only complaint is its acceleration... it not like a 2-smoke where you can rev it up/down/up/down/up/down (when edging for example).

I've heard that the 4-mix engines can be finicky with certain oil choices... or just internet folklore. By hot, you mean heat-soaked? Or just warmed up.

 

[The motor guy]

Originally Posted By: bmwpowere36m3
Which model Stihl?

I have a FS-90R and it runs great... first couple tanks at 40:1 with Stihl Ultra and 89 E10 and now 50:1. My only complaint is its acceleration... it not like a 2-smoke where you can rev it up/down/up/down/up/down (when edging for example).

I've heard that the 4-mix engines can be finicky with certain oil choices... or just internet folklore. By hot, you mean heat-soaked? Or just warmed up.


With the way I set it was almost identical to a 2 stroke, you could feather the throttle and slow the line down so you're not throwing things. Yeah I mean running it hard for 20 minutes trimming the side of a ditch or something. Without the guard on I only let out like an extra 4in of line total, but I'll notice that after the trimmer has been run hard and is good and hot that instead of me only using half throttle I'll have to keep it at full throttle to keep the rpm of the line the same.

It's the fs100rx

 

[bmwpowere36m3]

I can feather the throttle and modulate it, but its no where near as responsive as a 2-stroke.

You need to keep it at full-throttle to get proper cooling... if your running it hot and heavy with extra line, better keep it WOT. Why don't use run the guard and see how it runs.