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Thread: Stihl 4 mix starting problems POSSIBLE SOLUTION

  1. #1
    Senior Member Chris B's Avatar
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    Default Stihl 4 mix starting problems POSSIBLE SOLUTION

    I know Stihl has a terrible rep for starting issues especially on a hot day but I’ve found the reason (for me anyway) on the 4 mix kombi’s
    If you are having the same prob which I know at least a few are by what’s written on here then you will kick yourself for how simple it is

    We have two 4 mix kombi’s and never had starting issues.. nearly always first pull hot or cold, but eventually became hard to start.
    Anyway after trying everything
    ( I even rang Stihl and spoke to a technician who thought maybe was ignition module but I knew it wasn’t as both kombi’s had issue. Dealer didn’t fix anything either)
    ... plug/valves/carby clean/exhaust etc.. realised it was just a blocked air filter..


    But the reason why it gets blocked is the issue. It seems to be the breather from the fuel tank is vented to just behind the air filter... so if fuel travels back up the line it gets soaked reducing airflow to engine.. making hard to start (not to mention robbing power)
    Seems to be two causes.. if you fill up the tank too much it can force the fuel up the line when you put the lid on .. also hot weather makes the issue worse due to heat expanding air/fuel pushing fuel up the line even more.

    That explains why it is even more harder to start after a couple of jobs as the air filter gets more soaked as the day goes on.. even quicker when temps are warm. I’m guessing that usually not as bad the next morning as the fuel evaporates off.. but over time as it uses a 2 stroke mix the oil builds up in the air filter making it worse and obviously doesn’t evaporate.

    The worst thing is I always cleaned the air filter but you cannot see the fuel oil inside.. so the whole time I ruled out air filter as the problem.
    I realised the problem when I pulled the cord a billion times and it wouldn’t start.. pulled the air filter off .. started first pull

    Anyway to fix I soaked the air filters in degreaser and they are as good as new. To stop them getting soaked I fill up before a job (so they aren’t sitting in the toolbox with the heat forcing the fuel out) and when I fill up most importantly don’t fill all the way to the top.. have to leave some air in there.
    I find you still have to wash the filters but this problem is now gone. also keep a spare clean filter to swap over on the go.

    I’m assuming a couple ppl on here who said they had probs with starting after filling up and also another said that fuel leaked out in the toolbox are caused by the same issue.


    (note if your breather valve isn’t working this will also cause this prob)
    Also another thing with the 4 mixes if you’ve had them for a while and haven’t adjusted the valves make sure you do as you will find heaps easier to pull the cord to start as it has a mechanical decompression. standard feeler gauges dont fit the Stihl so you can either get your dealer to do it for you or what i did is ordered the valve adjustment kit.. its about $10 and includes gasket / washer and special feeler gauge. i just reuse the gasket and washers and keep the new ones as spares.

  2. #2
    Member of forum Stump's Avatar
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    Default Re: Stihl 4 mix starting problems POSSIBLE SOLUTION

    The factory issue filter is a throw away job, and shouldnt be washed according to my Stihl shop. Once the backing material gets soaked with oil,...chuck it. Buy a sponge type one, and wash that regulary Same with all of the Stihl gear, blower etc. My mechanic said most contractors rip them straight out upon purchase, and as a result he has boxes full of them.
    The other problems with them can relate to the spark arrestor.
    I want to die peacefully in my sleep like my Grandfather.....not screaming in terror like the passengers in his car!!!

  3. #3
    Senior Member Wombat Garden Services's Avatar
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    Lightbulb Re: Stihl 4 mix starting problems POSSIBLE SOLUTION

    Anyone got a part number for the sponge type filter ?

  4. #4
    Senior Member 4 Gardens's Avatar
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    Default Re: Stihl 4 mix starting problems POSSIBLE SOLUTION

    I found on my Stihl blower the spark arrestor was blocking up - unscrewed it and cut the mesh off - no probs now

  5. #5
    Senior Member DavidS's Avatar
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    Default Re: Stihl 4 mix starting problems POSSIBLE SOLUTION

    Thank Chris B for that information, I will file in back of mind for when I start having problems with my Kombi unit. It's pretty good at moment.

  6. #6
    Senior Member Chris B's Avatar
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    Default Re: Stihl 4 mix starting problems POSSIBLE SOLUTION

    had the same probs with my blower spark arrestor a week after i bought it but since then that's been all good. different setup to the 4mix though so have had problems with the air filter.

    regarding the sponge type filters i was actually thinking of cutting up a kitchen sponge and putting it in there but once i worked out the reason why it was getting blocked its been fine since. i just make sure always have a spare clean one just in case.

    its such a great machine when its running well so im happy now

  7. #7
    Senior Member HPM's Avatar
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    Default Re: Stihl 4 mix starting problems POSSIBLE SOLUTION

    You can buy filter foam from various suppliers and cut it to size... I get mine from Clark rubber or Briggs and Stratton make a foam block from the local mower shop. Heaps cheaper than genuine foam filters and you can afford to have a few spares.
    Hunterpropertymaintenance@gmail.com
    Work to live, life's too short..
    Specialising in small and Large area collection mowing with Walker Mowers.

  8. #8
    Senior Member happymowin's Avatar
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    Default Re: Stihl 4 mix starting problems POSSIBLE SOLUTION

    EXACTLY WHAT HAPPENS TO MY FS130 - the filter gets full of oil/fuel, the fuel evaporates, and youre left with an oily filter which wont start.

    i just blow the filter out with the blower when i want to start it, i dont use it all the time.

    have to ask the shop about the filter like you said.

    thanks for the info - i knew i had the problem but not why

  9. #9
    Senior Member Kathryn's Avatar
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    Default Re: Stihl 4 mix starting problems POSSIBLE SOLUTION

    my stihl HS45 had bee really hard to start, even if i took the air filter out and then the other day it started on the 2nd pull. im happy its going again but i wish i knew why.

  10. #10
    Member of forum Stump's Avatar
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    Default Re: Stihl 4 mix starting problems POSSIBLE SOLUTION

    The HS45 is a bit like that. Its the hardest thing to start in my kit. Fine once its warm. Usually 3 pulls with choke on, until it trys to fire, then choke off, and away it will go next pull. Mine needs a new filter now, as the blade speed is starting to slow. I pulled it out today and it was full speed ahead. It has the same type of filter as the Stihl 4 mix whippys, with the different backing stuff, that gets choked with oil. I need a sponge type for that one.
    I want to die peacefully in my sleep like my Grandfather.....not screaming in terror like the passengers in his car!!!

  11. #11
    MEMBER Fred's mowing's Avatar
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    Default Re: Stihl 4 mix starting problems POSSIBLE SOLUTION

    Quote Originally Posted by Chris B View Post
    I know Stihl has a terrible rep for starting issues especially on a hot day but I’ve found the reason (for me anyway) on the 4 mix kombi’s
    If you are having the same prob which I know at least a few are by what’s written on here then you will kick yourself for how simple it is

    We have two 4 mix kombi’s and never had starting issues.. nearly always first pull hot or cold, but eventually became hard to start.
    Anyway after trying everything
    ( I even rang Stihl and spoke to a technician who thought maybe was ignition module but I knew it wasn’t as both kombi’s had issue. Dealer didn’t fix anything either)
    ... plug/valves/carby clean/exhaust etc.. realised it was just a blocked air filter..


    But the reason why it gets blocked is the issue. It seems to be the breather from the fuel tank is vented to just behind the air filter... so if fuel travels back up the line it gets soaked reducing airflow to engine.. making hard to start (not to mention robbing power)
    Seems to be two causes.. if you fill up the tank too much it can force the fuel up the line when you put the lid on .. also hot weather makes the issue worse due to heat expanding air/fuel pushing fuel up the line even more.

    That explains why it is even more harder to start after a couple of jobs as the air filter gets more soaked as the day goes on.. even quicker when temps are warm. I’m guessing that usually not as bad the next morning as the fuel evaporates off.. but over time as it uses a 2 stroke mix the oil builds up in the air filter making it worse and obviously doesn’t evaporate.

    The worst thing is I always cleaned the air filter but you cannot see the fuel oil inside.. so the whole time I ruled out air filter as the problem.
    I realised the problem when I pulled the cord a billion times and it wouldn’t start.. pulled the air filter off .. started first pull

    Anyway to fix I soaked the air filters in degreaser and they are as good as new. To stop them getting soaked I fill up before a job (so they aren’t sitting in the toolbox with the heat forcing the fuel out) and when I fill up most importantly don’t fill all the way to the top.. have to leave some air in there.
    I find you still have to wash the filters but this problem is now gone. also keep a spare clean filter to swap over on the go.

    I’m assuming a couple ppl on here who said they had probs with starting after filling up and also another said that fuel leaked out in the toolbox are caused by the same issue.


    (note if your breather valve isn’t working this will also cause this prob)
    Also another thing with the 4 mixes if you’ve had them for a while and haven’t adjusted the valves make sure you do as you will find heaps easier to pull the cord to start as it has a mechanical decompression. standard feeler gauges dont fit the Stihl so you can either get your dealer to do it for you or what i did is ordered the valve adjustment kit.. its about $10 and includes gasket / washer and special feeler gauge. i just reuse the gasket and washers and keep the new ones as spares.
    Great post Chris, this is what we need more of.
    You worked it out yourself, while the dingbats in the shop would'nt have a clue, or dont care?
    Cheers Fred.

  12. #12
    Member Tender Lovin Lawn&Garden's Avatar
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    Default Re: Stihl 4 mix starting problems POSSIBLE SOLUTION

    Buy a honda there easy to start my son could do it when he was 4
    Tender Lovin Lawn and Garden Care
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  13. #13
    Senior Member Chris B's Avatar
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    Default Re: Stihl 4 mix starting problems POSSIBLE SOLUTION

    Quote Originally Posted by Fred's mowing View Post
    Great post Chris, this is what we need more of.
    You worked it out yourself, while the dingbats in the shop would'nt have a clue, or dont care?
    Cheers Fred.
    thanks, i never take stuff into the shop to get fixed but i thought that's what the experts are there for... took it in... picked it up .. took it back the next day.... (did that 4 times) and they couldn't find anything wrong with it so I almost gave up on Stihl's and their rep for hard starting !!

  14. #14
    Junior Member Phil 100's Avatar
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    Default Re: Stihl 4 mix starting problems POSSIBLE SOLUTION

    Excellent Post Chris, got to 37 degrees here in Adelaide today, got my FS 90, 4 mix out of the shed this morning and removed the Stihl air filter, didn't over fill the tank, started first or second pull all day. Tremendous thank you.

  15. #15
    Member keljad's Avatar
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    Default Re: Stihl 4 mix starting problems POSSIBLE SOLUTION

    being a STIHL patriot, with several STIHL machines (whipper snippers and chainsaws) that I inherted from dad and still goes as good as they did 20 years ago.........Im concerned at this post consideing that I just layby'd a STIHL 4 MIX Kombi unit. As Im in Darwqin, its hot all the time............will this cause me issues, and why is the 4mix different from STIHLs of old that still soldier on as good as the day they were bought (20 years later)

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