Chain saw won't stay running under load

Discussion in 'General Off Topic Forums' started by Andyman, Jun 2, 2013.

  1. Gibsonian

    Gibsonian AK Subscriber Subscriber

    Messages:
    3,195
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    Iowa
    Sounds like you need to adjust the high speed fuel mixture. Best way to do it is under load, at full throttle. Setting it to acheive the fastest speed under no load will lead to exactly what you are finding. I believe you are running too lean.
     
  2. bowtie427ss

    bowtie427ss arigato gozaimashita Subscriber

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    There should be 3, idle speed, low speed mixture, and high speed mixture. Sometimes the mixture screws will have an "H" and "L" cast in the carb body next to them.

    Before you tear into anything, back the high speed screw all the way out and shoot a shot of carb cleaner in there. Replace the high speed mixture needle(screw), screw it all the way in until it gently seats then back it out 1-1/4 turns. Wouldn't hurt to do both mixture screws, just don't mix them up.

    Ethanol levels are really beginning to raise heck with small engine fuel systems. For any small engine that's going to sit unused for more than a week, i strongly recommend emptying the fuel tank completely and running the engine until it sucks the carb dry of fuel and stalls.
     
    darksolstice likes this.
  3. Ed in Tx

    Ed in Tx Super Member

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    I did that with my weed trimmer. Drained, stored with a dry tank, let sit about a month, and the rubber grommet the hoses go through, and the cork gasket in the cap, all dried out and the thing leaked gas like a sieve next time I fueled it up. Just can't win.

    BTW a tip on removing those mixture screws: screw all the way IN first and count the turns til the screw seats, then when you put back together with the screw the same turns out from seated position, should be very close where it needs to be.
     
  4. bowtie427ss

    bowtie427ss arigato gozaimashita Subscriber

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    This relies on the assumption that it was where it needed to be to begin with. :D

    You know what happens when we rely on the assumptions of our fellow man. :yes:

    Seriously though, that is a good suggestion. I just use 1-1/4 turns as a rule of thumb starting point. Of course the final correct setting can and will vary from model to model and depending on the general health of the engine.

    As 2-stroke engines wear, the power loss comes as much from the reduced ability to pull vacuum and transfer, as it does from loss of pre-combustion compression.
     
  5. rswojo

    rswojo AK Subscriber

    Messages:
    957
    Inquiring minds want to know. When you find out what is wrong with it, post what you found.
     
  6. Andyman

    Andyman Scroungus Stereophilus Subscriber

    Will do!
    It's kind of on the back burner now though as we cut down the limbs with the Sawzall. Cindy asked the tree trimmers who were clearing the utility lines in the area if they would grind up our limbs with the trimmings they took off our trees and they did!!!

    All I have now is a 10" stump about 5' high to pull out and this will be past tense. I will mess with the carb as suggested here though and get back to all of those who have been so helpful here!!

    Thanks!!

    [​IMG]
     
  7. Tripod

    Tripod Well-Known Member

    Messages:
    940
    Location:
    Cape Town
    I run 3 petrol machines - the Weedeater blowvac and my Aussie Victa runs on leads additive fuel. My Homelite edgetrimmer runs on unleaded. The first two, will not run on unleaded.

    Anyway, the condition of your sparkplug's combustion end will tell you what's up. Dark and sooty = incorrect fuel to air ratio, ie running too rich or near flooding. Very light grey = running too lean.

    A rule of thumb for the sparkplug gap is usually 0.6mm.

    You should also look at the condition of the needle and its seat inside the carb. I had a bit of a problem with my Victa mower - much difficulty in starting.

    A close inspection of the needle and seat (plastic needle and brass seat insert) revealed a ring worn in the needle's tip. And pitted corrosion on the needle's brass seat insert so fuel was leaking past the needle valve, flooding the carburettor. Cure = re-polish the pointy part of the needle and hone the needle's seat with some 800grit 3M abrasive paper by folding it 2 or 3X into a cone.

    My oldest gas machine is now 37 years old. The Weedeater about 20 and the Homelite trimmer 8 years. How? Total avoidance of lawnmower repair shops and owner-operated:D

    Hehe...famous last words. I'm 70yo in a few days and don't know for how long I'll still keep on cutting, trimming and blowvaccing.

    tripod
     
  8. Olorin67

    Olorin67 Active Member

    Definitely running lean if its better with the choke partly on. If it idles, but does at higher throttle its probably a fuel delivery issue, like a metering diaphram. They can get too stiff with age or ethanol gas. A partly clogged main jet could do it, too. There are 2 fuel systems on most diaphragm carbs, idle and main. Your idle system is probably ok. Chenck the fuel line in the tank, could be cracked and sucking air, but then you would see bubbles in the line when you press the purge bulb. Dont run a 2 stroke if its running lean, you will burn it up and score the cylinder.. A if you take the diaphram cover off the carb- steel plate with 2 or 4 screws. You can see if its gunked up from old fuel. Ethanol fuels go bad real fast .. In a few months and get gummy.
     
  9. electronjohn

    electronjohn Plug it in & see!! Subscriber

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    2-stroke or 4-stroke...good fuel is #1. I use only 91 octane non-oxygenated gas in my mower & snowblower. And, even though they're both @#$%^& Tecumsehs they run like champs. Yah, it's over $4 a gallon...but for the small amount you have to buy it's money well-spent.
     
  10. Oerets

    Oerets AK Subscriber Subscriber

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    I still put premium in all lawn equipment.


    Seems to start easier for me.


    Barney
     
  11. mhett

    mhett Member

    Messages:
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    Location:
    Mid-Michigan
    check to see if the screen on the muffler is plugged with oil. I had a saw do this and it was that I was running it a little oil heavy-plugged the screen on the muff. Good luck.
     
  12. bhundu

    bhundu Addicted Member

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    Good work!
     
    Last edited: Jun 9, 2013
  13. rswojo

    rswojo AK Subscriber

    Messages:
    957
    Stumps don't come out very easily. You would be best off to hire or rent a stump grinder. I could take it out with my backhoe but the end result is a big mess. If you have more time than money a shovel and an ax will do the trick.
     
  14. 240sx4u

    240sx4u Lunatic Member

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    I cut down a very large maple tree with a crappy remington electric chainsaw. It caught fire right at the end. haha. The tree was so tall I had to climb it to top it out. The trunk was about 2 feet in diameter, and that's when I smoked that electric saw. That said, I don't use a gas one enough to keep it around the house. Seems like anything with a small engine won't start for no apparent reason from time to time. I just bought an electric weedeater for that very reason.

    Here's the saw I used, this thing is a little badass. http://www.sears.com/remington-tool...p-07141470000P?prdNo=1&blockNo=1&blockType=G1
     
  15. Oerets

    Oerets AK Subscriber Subscriber

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    On the stump, cut it as close to the ground as possible. Then drill holes and put salt peter in to the them. Cover up and wait till next year. That will rot the root out.



    Barney
     
  16. John James

    John James "Bob's your uncle" (Stolen) Subscriber

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    That's more or less what they told us in Basic Training (ARMY) back in the 70s!:D
     
  17. toxcrusadr

    toxcrusadr AK Subscriber Subscriber

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    No need to hunt down salt peter, it's just potassium nitrate, so use some lawn or garden fertilizer. It really does work - helps feed the microbes that chew up the wood. Unless you're fussy about appearance, just let the stump be there flush with the ground till it rots away.
     
  18. opa1

    opa1 Tenacious Subscriber

    Messages:
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    Location:
    South Texas
    I'm betting on a vacuum leak. Crank seals, case seam, cylinder base gasket, head gasket, carb to cylinder gasket. . A two stroke will not draw fuel with a leak. It might idle but will bog when throttle is applied. Check all bolts in these areas. These suckers vibrate alot. I've had cylinder to case leaks quite offen on older two strokes.

    Mark
     
  19. usedto

    usedto Lunatic Member

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  20. jimbofish

    jimbofish for TRULY GREAT MUSIC

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    Apparently you missed the backwoods Alaska show where they showed how to blow out a stump with blackpowder in a Mtn. Dew bottle? :scratch2: :D
     

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