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066 Magnum rpm question...

Discussion in 'Chainsaw' started by MotorSeven, Mar 8, 2009.

  1. MotorSeven

    MotorSeven Addicted to ArboristSite

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    I finally got around to putting the dual port muffler on my 066. After the install & before I changed the carb settings it was tacking at 13,800. My shop manual says 12K & using a Stihl tac I get 12,900 with the high limit screw all the way out to it's stop.
    Am I doing something wrong?

    I went ahead and milled a 17' pine log into 4x6 rafters for a shed I am building. It should have sailed thru the pine, but it actually seemd a little boggy & slow even though I had just sharpened the chain.

    RD
     
  2. Lakeside53

    Lakeside53 Stihl Wrenching

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    Stop? you have the carb limiters in place. Remove them them and retune..

    And... don't use the saw, particularly for milling, until you do - after the muffler mod....you're likely way too lean.
     
    Last edited: Mar 9, 2009
  3. MotorSeven

    MotorSeven Addicted to ArboristSite

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    Geeze, I hope I haven't screwed anything up. I didn't realize I had stops.....crap.

    RD
     
  4. Martinm210

    Martinm210 ArboristSite Operative

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    My 066 manual says setting the max RPM to 13,000 RPM...?

    12,900 might be fine if it's due to being rich. Did you have that distinct 4 stroke burble sound? It wasn't a lean surging type of sound was it?
     
  5. MotorSeven

    MotorSeven Addicted to ArboristSite

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    No, no surging. I have a shop manual & it says tune to 12k, then go 1/2 turn in. This is for 1000' above sea level & i'm at 1,200'. I bought the tac because I have a hard time hearing the things that most do when tuning by ear. The "light just has not come on" for me with carb tuning, but I keep reading/researching & working on it.
    Apprehension doesn't help because I know a "simple" tune job can result in disaster......

    Andy, ref the limiters do I replace them after removal, or leave 'em off? Is there a thread for tuning a milling saw? I am fishing thru the search results now.
    RD
     
    Last edited: Mar 9, 2009
  6. Dan_IN_MN

    Dan_IN_MN Addicted to ArboristSite

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    check my sig for carb tuning. Do I replace them after removal? Yes
     
  7. teacherman

    teacherman Addicted to ArboristSite

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    Those little caps can be pulled off with a drywall screw, thinner the better, and need to be stuck back on after you adjust the carb, because they help hold the adjustment setting. Gosh, if I were milling, I would "de-tune" it down to around 10K or so. I think I recall Andy* recommending that at some point in the past.

    * aka "Keeper of the Orange and White Flame":greenchainsaw:
     
  8. MotorSeven

    MotorSeven Addicted to ArboristSite

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    MH, your link isn't working for me.
    Teach, I did read in one of the threads that Andy does turn his saw down to 11K-11.5K and uses syn oil. I am going to pull the caps today & re-tune to 11.5.
    I've got the rafters up, need to mill another pine for the nailers under the tin roof. The tin arrives fri. This 32x16 drop shed will house all of my milled lumber
    for the house. I changed my mind & went from a log to a modified timber frame. Site work starts this spring, milling rafters, beams & sills now. I will be using the Woodbug mill for the beams & rafters & am looking for a band mill for the dimensional lumber.

    RD
     
  9. ShoerFast

    ShoerFast Tree Freak

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    Yes.....


    You can get 12,900 2 ways, *just right, and on the **way to lean side before it leans out, burns up and dies.

    Gas engines will burn all the fuel when there is to much space between the fuel partials (too lean, about 17:1 (pound per pound) and will burn on the richer side when there is enough oxygen in the charge to burn all the fuel (about 10:1 give or take).

    Best ratio is just a tad leaner then too rich,,,, or a burble out of the cut that runs smooth in a cut,,,or the fastest timed cut.

    * Best power is about 11:1 (give or take) going over that gives us a burble sound as we are hearing the effects of the flame getting quenched do to the lack of Oxygen.

    ** Too lean stinks, as we can smell the unburnt gas that was heated, but the flame front could not ignite it all. fuel rushing in an engine cools the combustion chamber, not having enough fuel runs very hot, combine that with excessive/unused O2 and the heat can attack engine parts.
     
    Last edited: Mar 9, 2009
  10. MotorSeven

    MotorSeven Addicted to ArboristSite

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    Shoe, thanks for the info. I just pulled the limiter caps, trimmed off the tab, reset both to 1 turn out, then tuned the high side to 11,320. I think I hear this burble that everyone talks about, but to be honest it will take someone to show me & demo it on a saw.

    "You can get 12,900 2 ways, *just right, and on the **way to lean side before it leans out, burns up and dies"

    This confuses me, I can't quite grab how 12,900 can be close to lean and just right. Call me "tacku'tarded", but man some of this stuff can be learned reading & studying, but for those like me I need the hands on approach. Now while tuning I did feel the damp like exhaust which would be the lean side right?

    I skidded down another pine log, so tomorrow....."Mill time!" Right now it's Miller time!"

    :cheers:

    RD
     
  11. blsnelling

    blsnelling Site Sponsor

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    Your saw will turn 13K and still 4-stroke unless there's something wrong with it. That's what it was designed to turn with no mods at all. With the dual port cover you'll likely find that it will run higher.

    Secure your tach to your saw so that you don't have to hold it. With the engine fully warmed up, hold the throttle wide open with one hand. Then with the other hand, turn the H needle in until you hear it completely peak out. This is what we call 4-stroking. Go too far and you'll hear it begin to loose RPMs. Do not leave the RPMs here!!!!!!!!!!!!!! Immediately back the H needle back out until you just begin to hear it "miss". This miss is what we call 4-stroking.

    Your saw will perform best when it has just a little 4-stroking at WOT when pulled out of a cut and left at WOT. This is when the saw is its hottest and leanest. If it doesn't have any 4-stroke coming out of the cut, you're probably a little too lean.

    For milling, you will want to richen it up a fair amount. How much I'm not sure since I don't mill. 10K would likely be WAY too much. I would probably set it where it just cleans up in the cut. Richen it up until it will not run clean in the cut and the lean it out a little at a time until it will. Hope this helps.
     
  12. MotorSeven

    MotorSeven Addicted to ArboristSite

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    Thanks Brad, I copied your post & will give it try on one of my smaller saws......

    RD
     
  13. ShoerFast

    ShoerFast Tree Freak

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    Like Brad mentions, if a saw is running 10K while it is to fat/rich, there is way to much fuel for the air and it '4-cycles' or sounds like a 4-cycle engine.

    If you were to slowly turn the 'H' screw in from too rich, the RPM's will rise, 11, 12 13, 14, 15 maybe if you let it, but that is passing thought what they call strockio-metric (spell check) or perfect, that is about 14.7 : 1 fuel ratio. (Perfect is not the best power, it's the best gas millage, or power per gallon, we want most power per engine)

    Keep the screw heading in or lean and the engine will again lean out to that 12,900 you mentioned before, again. the engine will lose speed when it dose not have enough fuel to burn during the full power stroke. (stinks/lean)

    Best power is more around 11-12 : 1 , reason behind the burble out of the wood, clears up in the wood, 'trick' is that at say 13K and burbling, (too rich) the saw lugs down in the cut to say 10K, a lugging saw has more firing pressure or effective compression as the crank is loaded making the engine work harder (needing more fuel) and the slowing of the engine with the same throttle plate angle makes the carb slightly less efficient, slightly leaning the ratio. (back to perfect/most power setting!)
     
    Last edited: Mar 9, 2009
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  14. diesel&coffee

    diesel&coffee ArboristSite Operative

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    Shoe !!!!!!!!

    That was one fine post! :cheers:
     
  15. excess650

    excess650 Addicted to ArboristSite

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    The 4-stroking is really obvious with both my stock bore 660 and BB 066. Both have DP mufflers.

    If you're having difficulty hearing this, find some big, hardwood and tune "in the cut". Find the sweet spot where the saw is the strongest, put the tach on with no load and see where it is. Try this with an 8 pin rim rather than 7.

    Andy recommends tuning richer(H out) for more fuel to enhance cooling. This will lower revs and max power a bit.

    Running more oil than 50-1 is recommended for milling. This is extreme duty for the saw and it will require more lubrication. I run 40-1 and haven't seen any evidence of too much oil in the mix. Some guys do run 25-1 or 32-1.
     
  16. MotorSeven

    MotorSeven Addicted to ArboristSite

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    Ahha, thanks Shoe, good explanation, I understand it now! Thanks..........

    RD
     
  17. Martinm210

    Martinm210 ArboristSite Operative

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    Thanks guys,
    I think I'm going to try the tune in the cut approach. That makes sense to me trying to get peak power and RPM while in the cut is pretty simple. Find a good knot free log and make a cut being careful about pressure consistency, then turn the H screw out or in little bits and make additional passes until you have what turns the highest RPM.

    Then you could simply check for sound/max RPM without load, but it would be optimized for where it counts (in the cut).:clap:

    I've got the limiter caps off both my 066 and 044 builds, now I just need to go find some wood to make chips out of....:D
     
  18. Lakeside53

    Lakeside53 Stihl Wrenching

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    and... when you find "max", back it off a little. You NEED a safety margin...
     

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