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Chainsaw won't idle


walshie
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I have small Stihl MS171 that I use for limbing and a few bits and pieces. It was starting to play up - not idling, bogging down when I tried to rev it etc. I bought a few parts that needed changing anyway and gave it a bit of a service.

I read about cleaning out the spark arrester, but it doesn't seem to have one. (The book said they don't all have them), so I gave the whole thing a good clean, new sprocket and chain, new air filter, fuel filter and plug.

I started it and it fired right up. It revs great but then it wouldn't idle for more than a few seconds. More reading and it suggested setting the carb settings back to stock settings. I've done that and it starts easily enough, it revs easily enough, but it won't idle at all now. 

Any ideas?

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5 minutes ago, walshie said:

I have small Stihl MS171 that I use for limbing and a few bits and pieces. It was starting to play up - not idling, bogging down when I tried to rev it etc. I bought a few parts that needed changing anyway and gave it a bit of a service.

I read about cleaning out the spark arrester, but it doesn't seem to have one. (The book said they don't all have them), so I gave the whole thing a good clean, new sprocket and chain, new air filter, fuel filter and plug.

I started it and it fired right up. It revs great but then it wouldn't idle for more than a few seconds. More reading and it suggested setting the carb settings back to stock settings. I've done that and it starts easily enough, it revs easily enough, but it won't idle at all now. 

Any ideas?

unbolt the exhaust off the cylinder and check your exhaust port is not blocked up with carbon build up ,also there is usually a small mesh filter before the needle valve inside the carb which could be gummed up.

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there shud be 3 screws..........2 will be the air fuel mix hi/lo.......3rd will be the throttle screw...just start it and slowly screw it in so you get a spritley tick over...if it wont tick over and keeps fading ...the mix screw needs adjustment...........

i did the same thing on my leaf blower today (sthil)....jobs a gooden...first time ive touched it in 2 years..

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8 minutes ago, walshie said:

I have small Stihl MS171 that I use for limbing and a few bits and pieces. It was starting to play up - not idling, bogging down when I tried to rev it etc. I bought a few parts that needed changing anyway and gave it a bit of a service.

I read about cleaning out the spark arrester, but it doesn't seem to have one. (The book said they don't all have them), so I gave the whole thing a good clean, new sprocket and chain, new air filter, fuel filter and plug.

I started it and it fired right up. It revs great but then it wouldn't idle for more than a few seconds. More reading and it suggested setting the carb settings back to stock settings. I've done that and it starts easily enough, it revs easily enough, but it won't idle at all now. 

Any ideas?

If it's like a newish Top Handle i went through the same thing only to find out that it has to go to a Sthil dealer to be reset by plugging into a computer with the program on Not happy

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55 minutes ago, Walker570 said:

Ditchie as usual gives best advise. It is probably down to adjustment.  My 170 is also a bit grumpy on initial start but once allowed to run for 30 secs or so settles down and will tick over happily. The 170 and 171 are cracking little saws and with the right bar and sharp chain will cut well above their weight.

all my sthils........need to get warm before they settle....  what i have done in the past is to half fill the tank after emptying with pure fuel and pump it thro the carb and leave it overnight....pump it thro the carb again in the morning...tip it out and put in mixed oil/fuel...pump it thro and start it....somet9imes the carb will get gumbed up with infrequent use...

Edited by ditchman
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19 minutes ago, ditchman said:

all my sthils........need to get warm before they settle....  what i have done in the past is to half fill the tank after emptying with pure fuel and pump it thro the carb and leave it overnight....pump it thro the carb again in the morning...tip it out and put in mixed oil/fuel...pump it thro and start it....somet9imes the carb will get gumbed up with infrequent use...

I've done similar with my saws especially when they have sat for a bit and the pure fuel definitely seems to clean everything through. 

If they've really struggled I've even turned them over VERY briefly (as in less than a second) on neat and then left overnight and that's sorted it.  Having said this my saws are cheap so they either run or die, i probably wouldn't do it with something quality.

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I've always been very particular to let it run dry when I'm leaving it for any length of time precisely so it doesn't have 2 stroke sitting in the carb. Just seems odd that it starts and revs fine but won't idle. As Ditchman says, it's probably a mixture problem, but as the settings are as per factory, I have no idea which way to turn what. If I could get it to idle even roughly, I could tune it from there, but not running it's all guesswork. 

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I've only ever ran all my two smokes on aspen2.  Very expensive but I don't use too much a year and it keeps the seals and rubbers supple. When I mixed the fuel and oil for Stihl saws I was guilty of adding a little more oil to the mix.

The older sthil are better made than the new stuff.

Luckily I bought a Husqvarna 71cc 365 X-Torque saw just before they all went ECU. The ARB boys loved they're new saws until they couldn't do anything apart from back to dealer for plugging in to computer. 

It's the way all modern engines are going.

A good spray of carb cleaner could help. 

I find this fella very good to watch, this video should help.

 

Edited by figgy
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8 hours ago, walshie said:

I've always been very particular to let it run dry when I'm leaving it for any length of time precisely so it doesn't have 2 stroke sitting in the carb. Just seems odd that it starts and revs fine but won't idle. As Ditchman says, it's probably a mixture problem, but as the settings are as per factory, I have no idea which way to turn what. If I could get it to idle even roughly, I could tune it from there, but not running it's all guesswork. 

Figgy beat me to it. 

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Sliding slightly off thread, has anyone on here tried the battery operated chainsaws. Watched a video on you tube comparing the Sthil and the Worx and was impressed with their cutting ability. Not that I want another one, four already including a cord fed electric Titan which is brilliant but only if there is a three pin plug nearby.  Just wondered how long batteries lasted.

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8 hours ago, Zapp said:

Maybe invest in some Aspen, if it wont run on that you can be more assured the mix is/isn't the problem 

Never heard of it. I'll have a look now.

 

13 minutes ago, mellors said:

I've had it with my ms171. Changed filter, plug, tank filters, fitted carb service kit. Runs fine now. Apparently the carb diaphragm is critical on the them drys out and causes poor running and starting. 

👍

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Aspen 2 is an alkylate fuel and can stay fresh for several years. One of the main benefits is that it doesn't contain ethanol like pump fuel and this can cause problems in machinery that isn't frequently used. (Ethanol can absorb water and damage some plastics and rubbers.) Other brands are available such as Stihl's MotoMix which is what I use in my Stihl Saw.

Having said that, my little MS170 has gradually become harder to get it to idle without stalling until the saw has had half a tank through it.

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22 minutes ago, 243deer said:

Guilty as charged until I purchased one of these. Only making up 2 stroke as you need it from fresh fuel at the correct mixture does help things run well. 

 

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Thats a good idea, will look into getting one instead of mixing a gallon at a time.

Mick

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