STIHL 026 Bogging Down

Discussion in 'Shop Talk' started by Ken Scharabok, Jun 16, 2006.

  1. Ken Scharabok

    Ken Scharabok In Remembrance

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    After the overhaul of the piston assembly I used this saw to cut up three rather large downed trees, and some other work. However, now it is acting odd. Will start, sound fine, and work for a couple of minutes, until it gets warm. Then it loses power when cutting. No particular problem restarting. Good rpm until it starts to take a load. Replaced gas filter, cleaned air filter and replaced spark plug. No improvement. Seems like it is getting enough gas to run, but not cut.

    Suggestions/comments in kitchen English please - I'm mechanically disadvantaged.
     
  2. agmantoo

    agmantoo agmantoo Supporter

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    Ken, the symptoms are concerning since the saw was opened internally. It sounds to me as if the piston is attempting to seize. Not to insult but to verify, you do have enough of the correct oil in the gas, right? No ethanol blend gas for the 2 cycle enginers either. The reassembly went good and you got all the fasteners properly secured? Possibly you could look through the exhaust and the plug hole and observe the wall of the cylinder for gouging or scoring.
     

  3. Ken Scharabok

    Ken Scharabok In Remembrance

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    Yes, I am positive on the oil to gas mixture. Same as I use in my STIHL weedeater.

    Will try the cylinder inspection.
     
  4. ponyboy123

    ponyboy123 Well-Known Member

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    Just a thought, was having trouble withmy stihl 039 and took it to dealer. he took the front cover off the muffler, there is a filter inside to draw warm air to carb. he burnt it out cleaned it with commpressed air, reinstaled and saw worked great. might be worth a try.
     
  5. Ken Scharabok

    Ken Scharabok In Remembrance

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    I took off the muffler and did see a bit of scoring on the inside of the cylinder walls. However, just appears to be scratches and not grooves - at least the sides I can see. Piston moves freely up and down in cylinder.

    Muffler is at opposite end of saw from carburetor. Really isn't much. One empty chamber with a cover plate with one hole, screen and then a baffle. Screen is not clogged. Doesn't appear to be anything missing from it.
     
  6. fixer1958

    fixer1958 None of the Above

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    I would check for a possible crack in the fuel line. Sucking air under a load.
    Or, a carb diaphram stiff or cracked.
    Or, carb mounting loose or cracked.
     
  7. agmantoo

    agmantoo agmantoo Supporter

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    Ken, increase the oil in the gas a bit and see if you observe any difference. Did you have any problem getting the rings back into the cylinder? Any chance a ring is broken? Did you observe the scratches in the bore when you first took the engine apart? Since the engine starts easily and runs fine with no load the only other thing that comes to mind is to open the high speed jet setting slightly. I would add more oil first as insurance. PS,,,you are observing lots of air blowing over the cylinder and the area is not filled/clogged with sawshavings?
     
  8. mink

    mink Well-Known Member

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    might be a kinked fuel line.....but the scratches on the piston sounds scary to me...mink
     
  9. insanity

    insanity Well-Known Member

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    Heres a couple rambling ideas that crossed my mind. :D
    Wondering if the cylinder was bored and mated with a new piston of the wrong size?And also if the ring end gap was set correctly.If its to tight id think it would cause that problem as it got warmed up?

    If the carb isn't set properly it will not have enough power under load and can also damage the engine in the long run.
    Our local Co-op that sells and works on Sthil saws and trimmers can not adjust carbs worth a darn lately.(apparently some mechanics just dont care if its set properly or not) Last time i took it in i told them to leave my carb adjustment alone,but they didn't. Making that twice Ive had to reset it myself to even get it to start and run after getting it back.Last time the guy busted the caps off the needles so he could turn them out to like 5 turns. :flame: I swear I'm going to go postal on them if i ever have to deal with warranty work threw them again. :grump:

    If a gasket didn't seal it can suck in air, making it run lean.Which will cause the connecting rod bearings to run out of lubrication and cause it to scare the cylinder walls and or totally seize the piston.They can be leak tested for this.Oil leaking from a gasket area can also be a sign.

    Theres a web site with great instruction on setting chain saw carbs.But i cant think of its name. (The guys name , followed by Pro Saw or something to that affect.Anyone no of the site I'm talking about?
     
  10. Blu3duk

    Blu3duk Well-Known Member

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    replace the fuel line both on the inside of the tank and the outside. I had an older stihl that the fule line looked good but when you wrapped the rpm up it did the same as you sed, no leakage but it sucked air..... they make fuel lines to replace but we just use regular clear fuel line [cause its small enough OD] and its easy to replace with a good line/hose plier..... a needle nose also works.

    you may find something else needed, like unscrewing the gas cap, and puttig a whole new saw under it! but it probably is simpler than that.

    William
     
  11. Ken Scharabok

    Ken Scharabok In Remembrance

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    "Heres a couple rambling ideas that crossed my mind.
    Wondering if the cylinder was bored and mated with a new piston of the wrong size?And also if the ring end gap was set correctly.If its to tight id think it would cause that problem as it got warmed up?"

    The cylinder assembly was an aftermarket bought off eBay. Rings which came with it broke during installation (as if they were oversized), so my mechanic purchased 026 rings from a Stihl dealer to get it back in operation.

    "You may find something else needed, like unscrewing the gas cap, and putting a whole new saw under it!"

    Have pretty well made the decision to go that route with a new Stihl 260 PRO. I purchased the 026 10 1/2 years ago and, if were a car engine, I'd say it had about 250K miles on it. One summer I went through eight gallons of bar oil cleaning out fence rows. Its been a sometimes reluctant, but fairly reliable workhorse. Probably time to pass it on for parts.
     
  12. swamp man

    swamp man Well-Known Member

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    I know you checked it already,but I've had sooo many 2 cycle engines show the same symptoms,and it usually turns out to be a clogged muffler.Could also be an improperly adjusted carb,or dang near anything in the fuel system,for that matter.
    That said,I just can't say enough about the MS 260 pro.I run a fairly long bar on mine,changed out the sprocket for more low-end(she has high-end to spare),threw a yellow lable chain on,and that thing can reall toss the chips!If I'm not mistaken,they have a chrome-lined cylinder bore.If you do get one,I'll bet you'll be real happy with.
    Edited to add-I like the newer fuel/bar oil cap design,and the chain tension adjustment screw is located in a much more convenient spot on the new models.
     
  13. Ken Scharabok

    Ken Scharabok In Remembrance

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    Any chance it is the clutch?

    I took off the muffler. Sooty, but no obstructions I can find. Screen is in good condition and not clogged at all.

    Saw has been a trooper for me and I kind of hate to get rid of it, but...
     
  14. insanity

    insanity Well-Known Member

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    If it was the clutch i suspect the engine would still turn high rpms but the chain would not keep up when cutting.? Note i only [suspect] i dont no for sure as ive never had a bad clutch to deal with.

    With a new cyclinder it should be good for a few more K-miles id atleast have her looked at by a mechanic before i bought i new saw.Well ok so if it where me id buy the new saw anyway.Cause i love new saws! :D But you never no when you might need a back up saw to free a new stuck one. :hobbyhors
     
  15. Blu3duk

    Blu3duk Well-Known Member

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    nope it is a fuel and air mix problem..... fuel line, carb jet, or actual ignition.... if the electronic ignition goes out on those saws then they are toast cause you can buy a new saw for the price of that part alone [ok it only seems that way] but what you are talking about is mostly fuel related powersaws are just about as simple as it gets for fixing mechanical problems..... ok so i started running them way to young.....

    does it give the same problems if you leave off the airfilter? and is the trigger assembly pinching the fuel line or even close to it?

    something sounds to be starving the fuel air mix on the high end jet adjustment...

    blueduck <-------who might might have a screw loose once in awhile

    William
     
  16. Ken Scharabok

    Ken Scharabok In Remembrance

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    Acts the same with the air filter off. Trottle linkage is well away from fuel line going to carburetor from what I can tell. With filter off you can see trigger operating the valve in the throat. Once it started bogging down I open the high end jet screw a turn at a time to full open. No change.
     
  17. ericjeeper

    ericjeeper Well-Known Member

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    when revving it up.. does it run better or worse if you choke it ?
     
  18. Ken Scharabok

    Ken Scharabok In Remembrance

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    Tried it. Seems to run marginally better choked.

    Added: A couple of days before this started I left it in the pickup bed and it got rained on overnight. Next day it was harder than normal to start and then ran at only about half speed (no high rpm on trigger) until it was warmed up. Then worked normally for that morning's cutting. Problem started, as I recall, next time I tried to use saw. Could the electronics have been damaged by the rain?
     
  19. Blu3duk

    Blu3duk Well-Known Member

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    It is possible however not probable.... I know sawyers that leave saws in their strips to save packing them in and out up and down hillsides several hundred feet/ or a couple miles [highlead ground right of way and helicopter ground] and they are basically left out in the weather usually the bar is stuck in a high stump to keep off the ground in case it snows a bit overnight..... is my reason for saying not probable in all cases..... my saw gets wet just in the back of the truck sometimes.... but never hurt it...

    but if it runs it still seems to be fuel not lectrical...... the jet not geiving ou any difference may be the whole problem..... sounds like it is plugged, maybe a spot of dirt in it.... nuthin complicated.

    William
     
  20. fixer1958

    fixer1958 None of the Above

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    You sorta said it worked ok when you first used it and then it started having problems.
    I still think it's a fuel line or a plugged jet or diaphram that's stiff.