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Adjusting Carburetor

Post in 'The Gear' started by Mass. Wine Guy, May 27, 2010.

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  1. Mass. Wine Guy

    Mass. Wine Guy Feeling the Heat

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    When I replaced the spark plug in my Jonsered 535 the tip was very dark brownish. My understanding is that this indicates the saw's fuel mix is running too rich. I know where the high, low and idle adjustment screws are, but I've never adjusted this before. What's the best and simplest method?

    Thanks.

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  2. smokinj

    smokinj Minister of Fire

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  3. Mass. Wine Guy

    Mass. Wine Guy Feeling the Heat

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    How do I get to the spark arrestor to see if it's clogged up? Do I need to remove the muffler or is it just attached to it?
  4. kruger

    kruger Member

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    Smokinjay,

    I run an older (West Germany) 048. I've been cutting at about 6500' and having trouble keeping idle. I rev well and cut great in midrange RPMs and high end RPMs, but when I get out of a cut and decelerate the engine, I will sometimes kill it. I have to feather the throttle to keep the idle. I've adjusted the low everywhere it will go and can't seem to get it to idle. I have the low dialed all the way up and still have trouble keeping an idle. You seem like knowledgable Stihl man, what's the deal with my 048?

    P.S., I was told by a Stihl dealer to replace this saw with a new 460 when I was hunting down an aircleaner, but that was about 40 cords ago. Other than the idle, the saw will bury my dad's new 361.

    WYO
  5. kruger

    kruger Member

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    Wine Guy,
    Didn't mean to tread on your thread. I figured we are asking similar questions. Sorry, WYO
  6. smokinj

    smokinj Minister of Fire

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    I would pay with the hi idle screw listen to the sound wave and make sure the hi idle is set right then you should be able to dial the L screw in a little better. Your h screw will always be differnt each time you cut at that kind of heights so set it everytime you cut.
  7. smokinj

    smokinj Minister of Fire

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    yes remove the front cover and check it.
  8. Mass. Wine Guy

    Mass. Wine Guy Feeling the Heat

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    Well, I removed the muffler but saw no spark arrestor screen at all. I bought the saw in Canada, so maybe it wasn't required there. One less thing to worry about, but it was good experience removing the muffler.
  9. kruger

    kruger Member

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    I don't have an idlespeed/throttle stop on the saw...at least not on the external adjustment (outside on cover). I probably have one on the actual carb, but I haven't looked very close. This isn't a problem on the hardwood cuts in Western Nebraska at 3800'.
  10. smokinj

    smokinj Minister of Fire

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    only need one if you in a very dry forest, how did the piston look?
  11. Deere10

    Deere10 New Member

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    What ratio are you mixin oil and gas at? What octane gas??
  12. Mass. Wine Guy

    Mass. Wine Guy Feeling the Heat

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    Piston? Uh oh. I didn't look. I can look again. Is the piston inside of the small square opening I see when I remove the muffler?

    I mix a 2.6 oz. bottle of 2-cycle oil with 1 gallon of 89 octane gasoline.
  13. smokinj

    smokinj Minister of Fire

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    I run the highest I can get at 50:1
  14. kenskip1

    kenskip1 Member

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    WG, If the plug is a brown color then this is near ideal setting. A rich mixture would be on the black side.Check to make certain that the air filter is clean. A dirty one could give you a false indication, Ken
  15. LLigetfa

    LLigetfa Minister of Fire

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    Agreed.

    Not the same as plugs on a car.
  16. Mass. Wine Guy

    Mass. Wine Guy Feeling the Heat

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    Hmm. Maybe I should have left well enough alone, then. Now, after I "adjusted" the carb, the saw doesn't consistently run at full throttle when I have the throttle wide open. Then there are moments where it will suddenly reach the max and sound normal.
  17. LLigetfa

    LLigetfa Minister of Fire

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    Hmmm...

    It's always a good idea to count how many half turns the jets are set to so you can get it back into the ballpark should you get too far off.
  18. smokinj

    smokinj Minister of Fire

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    Are you tuning by ear or with a tack? And you can tune in the cut as well, but you probally dont have it tune right out of the cut.
    Dont worry about where the screw is wot until it sound prefect then back of enough to get a slight miss sound. If that doesnt bring it into tune do the same in the cut to almost perfect on a full load.
  19. Mass. Wine Guy

    Mass. Wine Guy Feeling the Heat

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    I tried adjusting my carb, but the saw still seemed slow and underpowered at high throttle under load, so I took it to a local small engine repair guy. If it's better when I get it back I'll pay attention to its sound.

    What's the deal on using tachometers? Do you adjust the carb strictly by the numbers? Amick's has a $28 digital tach.
  20. EatenByLimestone

    EatenByLimestone Minister of Fire

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    I just had a friend adjust my saw. He said it was running a bit lean. I guess it was set lean from the factory or leaned out as the saw was broken in. It now runs much smoother from startup.

    Matt
  21. RobC

    RobC Minister of Fire

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    Newer saws do get a break in period and then they can have the carb set again at a higher speed after some good cutting. Just a suggestion, let a good saw mechanic do it. If you get your saw to lean you can loose the lubricating capacity of the 2 stroke oil and seize saw or loose all your compression from worn rings. Some saws between the cylinder head and the carb area there is slide plate and hole for summer or winter run. Allows for different air temps to enter carb.
    Rob
  22. smokinj

    smokinj Minister of Fire

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    yes, it will get you very close but still good to be able to hear the slight 4 stroke.
  23. Mass. Wine Guy

    Mass. Wine Guy Feeling the Heat

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    Is this shen the engine sounds kind of rough but still runs really well?
  24. smokinj

    smokinj Minister of Fire

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    yes once it sounds perfect then back off a little its called 4 stoking.
  25. LLigetfa

    LLigetfa Minister of Fire

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    To me, the term "back off" sounds like the wrong direction. You need to go in the other direction and open (richen) it up a little.
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