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About 4 stroking

Discussion in 'Chainsaw' started by Buffco, Dec 11, 2009.

  1. Buffco

    Buffco ArboristSite Lurker

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    I've read a lot on the muffler mod threads and tuning threads....

    I see a lot of mention about a chainsaw "4 stroking". Can someone explain why that is ideal or not, and how can you tell when the saw starts doing it?

    I'm assuming there's a sound you listen for.....
     
  2. striperswaper

    striperswaper AboristSite Guru

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    do a search on here there is plenty, vids w/ sound...
     
  3. jus2fat

    jus2fat Two Harley Fatboys

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    The term is used as the sound of the saw while idling and warmed up and being used to cut. It's about the high speed setting adjustment. In tuning the carb, one would set the low speed adjustment first...just ever so slightly rich. This would be while at normal idle. Then you set the high speed while saw throttle is wide open (WOT)...Turn it clockwise (lean) until you get a high smooth rev...then turn it back counter clockwise just until you hear it change to a slight "gurgle" sound that is referred to as "four-stroking". It's not real smooth as when it was at high revving. Again, it is being set just ever so slightly rich. Now you turn the screw back toward clockwise (lean) until the carb just clears out again.
    Now if you did this correctly...when you pull saw out of a cut and drop saw back to idle it will again "gurgle-four stroke"--but when you start another cut the carb will clear back out and rev smooth but is still set on the rich side.
    The high speed needs to be set rapidly as you don't want to be holding the saw at WOT while not in a cut but for only a few seconds!!!!!!

    This will explain it perhaps better for you than I did....

    http://www.madsens1.com/saw carb tune.htm


    J2F
     
    WetGunPowder and FATGUY like this.
  4. bullittman281

    bullittman281 ArboristSite Operative

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    Hello,
    I set my saw up so that as soon as I start cutting the engine "cleans up" and sounds really crisp. If its not in the cut I have it rich enough to burble. The best way to hear the change that the saw makes is to fire it up and get the high setting very rich. The saw will run poorly and sound rather rough. Start bringing the Hi screw in and the revs will come up and eventually you will find max revs and the engine sound will clean up. DO NOT set it for max revs! From the clean sounding max RPM as you turn the Hi screw out the engine note will make a distinctive change. That change is when the saw gets rich enough to start four stroking. At this point your fairly close to where you need to be. If in doubt make it a fuzz richer. your clue to being way too rich is the saw will try to four stroke in the cut. As soon as you start cutting the engine should clean up and sound crisp. If it still sounds rough you are way too rich. To my knowledge rich only fouls plugs and mufflers. I don't think that rich will cause any real engine trouble with in reason.

    True story here. This fall I was helping a bunch of coworkers clear out a bunch of elm trees. One of them drug along their 372xp Husqvarna or something like that. They fried it cutting up this massive stump from not setting the carb for conditions. I had to fire up my PP 295 to finish the job because it had the longest bar on a running saw. I ran several tank fulls through the poulan at wide open throttle cutting this thing up. Thats wide open for and entire tank of fuel, not ever letting off. This stump was Huge! I set my carb up for the conditions of the day and keep and ear to it in case something changes. Talking with the guy later on I found out that he just stuck a replacement carb on it and ran it, never turning an adjustment screw. Somehow the carb was set close enough to at least run. He got away with it cutting up at high elevation but at 4,000Ft it killed his saw. DON'T let them run lean and you'll be good to go.
     
  5. bitzer

    bitzer Bullshit Timber Expert

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    Yep, always check your saw for tune after its warm especially if conditions are different from the last time it was run. It only takes a few seconds, just lift it out of the cut and drop it back in and it will save a major PITA situation later.
     
  6. bitzer

    bitzer Bullshit Timber Expert

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    When four stroking at WOT off load there is a little extra fuel that is not being used, when the saw is placed into the cut the fuel is used. If the extra fuel where not there the saw would be too lean in the cut and over heat.
     

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