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What RPM should my Stihl's hit for MAX HP!?

Discussion in 'Chainsaw' started by ApexTreeService, Nov 12, 2009.

  1. ApexTreeService

    ApexTreeService ArboristSite Operative

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    I just took my MS390 and MS192 to the shop today and the tech leaned the top end on them to hit 12,500 rpm's. That sounds a bit slow to me, shouldn't they be leaned to hit 14,000 rpm's unloaded???
     
  2. blsnelling

    blsnelling Site Sponsor

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    I believe the spec on both is 13,000.
     
  3. ironman_gq

    ironman_gq Addicted to ArboristSite

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    unloaded rpm isnt what matters however it is a good way to tune. Its the max rpm that it can hold loaded in the wood that matters
     
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  4. Guarddog1

    Guarddog1 AboristSite Guru

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    It is always fun to see how high a saw will rev however I have found that max rpm usually equals lean in the cut. I usually adjust for max rpm then hit the wood and it always seems I adjust richer in the wood and that makes sense a saw does not make peak power at peak rpm.Each saw is different as well depending what is done to it. According to shop manual the 039 Max. permissible engine RPM is 13000 max torque is reached at 6500 but keep in mind a muffler mod or so will change this.
     
  5. mountainlake

    mountainlake Addicted to ArboristSite

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    May as well go to 14500 just to make sure you burn them up. Steve
     
  6. timberwolf

    timberwolf Addicted to ArboristSite

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    390 should be making maximum HP when loaded to around 9000-9500 RPM.

    To figgure out how tuning for 9000-9500 loaded relates to WOT no load RPM. set it at factory spec time some cuts, then richen it to bring the RPM down say 250 RPM make some more cuts and check the time, then lean it to take it a little over factory spec and provided it is still sounding OK make some more cuts. When you get the saw cutting the fastest back it off a hair as a safety margin.
     
  7. mountainlake

    mountainlake Addicted to ArboristSite

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    Good advice TW, you'll find saws cut the fastest with a little more fuel rather than really screaming with no load. Even the factory specs might be on the lean side due to EPA regs. Steve
     
  8. timberwolf

    timberwolf Addicted to ArboristSite

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    Yup, though the ideal air:fuel ratio for low polution and maximum fuel ecconomy might be 14 to 1 or so, gasoline will produce maximum horsepower burnt down closer to 12:1.

    The bar chain and wood will factor in also in the ideal carb settings. It is possible to run leaner in smaller wood or with more efficient chain.
     
  9. lone wolf

    lone wolf Tree Freak

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    max rpm

    are you racing or working they tune em a bit under at the dealer for a reason so you don't squeak them.you prob can go higher on the ms 200T that is in my signature that saw likes to scream.
     
    Last edited: Nov 13, 2009
  10. Del_

    Del_ Tree Freak

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    Speaking of the 200T.....


    It has the needle adjusting stops just like other Stihl saw doesn't it?


    I've got one that's screaming a little to loudly and have been thinking of removing the stops.

    Any tips?

    I removed the stops, shaved them and reinstalled on my MS460 just last week and it was easy. I'm hoping the MS200 is as easy.
     
  11. lone wolf

    lone wolf Tree Freak

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    ms 200t

    best money making saw for a tree service there is. did you open up the exaust and have you put a tach on it ?you click on the link on my sgnature?the ms 200t is my fav.might want to let a bit more gas in.yes it has a limiter on the high jet.
     
    Last edited: Nov 13, 2009
  12. blsnelling

    blsnelling Site Sponsor

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    He asked about tuning his saws. Tuning at WOT is how it's typically done. Factory specs are +- several hundred RPMs. He didn't mention that they were modded, so I assumed they were not. If you tune a stock saw to factory specs, it will be slightly rich no load.
     
  13. Del_

    Del_ Tree Freak

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    Thanks!

    ....and I grabbed the pdf.
     
  14. ApexTreeService

    ApexTreeService ArboristSite Operative

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    The MS 200 only has the screen removed, I need to mod the muffler this weekend. Any quick fixes for that? On the MS 390, I removed the screen and deflector, and drilled a 3/8 hole in the muffler. I just removed the screen and deflector on my MS 192, and honestly it seemed like it did have more usable power. In fact, same goes for the MS 390, and the MS 200.

    I'm new to performance tuning (most work done with a saw in a given period of time, i.e. HORSEPOWER) on the size of two strokes used in chainsaws.

    I have done RC car tuning where you richen or lean the top end after running it in/on a given condition/day then testing the head temp with a gun, too hot, too lean, too cool, too rich and not enough power. I'm sure something has to translate, but I don't see anyone with pyrometers on the head, or using a gun.
     
  15. ironman_gq

    ironman_gq Addicted to ArboristSite

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    You tune saws so they just four stoke unloaded and clear up as soon as they are in the cut. Use the search to find the precedure
     

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