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Stihl's 4 mix engine?

Discussion in 'Chainsaws and Power Equipment' started by Marshel54, Jul 13, 2017.

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  1. Marshel54

    Marshel54

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    In a conversation before a the GTG at Dennis's the general consensuses was that I could use 40:1 gas in my Stihl saw. The 50:1 was to meet EPA standards. I mixed my 40 and 50 gas to empty a can. The saw runs good on that gas.
    I bought a Kombi 4 mix. Does the same thing apply to it?
    I don't completely understand the mixed four stroke theory.
     
    Marshel54, Jul 13, 2017
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  2. TurboDiesel

    TurboDiesel

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    the "4-mix" requires a 2 cycle mix, but it's actually a 4-stroke engine, complete with camshafts, pushrods, valves, rockers and valve springs...

    it does NOT have a crankcase for oil-lube, so lube must go through the engine.
     
    TurboDiesel, Jul 13, 2017
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  3. Marshel54

    Marshel54

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    From what I am gathering from your post, a little heavier oil mixture should not hurt the engine. I need to use up that jug of gas.
     
    Marshel54, Jul 13, 2017
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  4. Redfin

    Redfin

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    I run 40:1 in my 131. No problems.
     
    Redfin, Jul 13, 2017
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  5. clemsonfor

    clemsonfor

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    No that will not hurt it. You can run it at 32:1 as well and not hurt it
     
    clemsonfor, Jul 13, 2017
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  6. 94BULLITT

    94BULLITT

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    4mix engines have carbon issues. The more oil you mix the bigger a problem this is going to be. Some oils are worse than others. I say go with the manufacturers recommendation of 50:1 on everything.
     
    94BULLITT, Jul 13, 2017
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  7. clemsonfor

    clemsonfor

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    That's why I should of said I would use a good proven synthetic oil.

    Little to no carbon issues from them.
     
    clemsonfor, Jul 13, 2017
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  8. TurboDiesel

    TurboDiesel

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    I Usually run mine around 40:1.
    A little extra oil is always better
     
    TurboDiesel, Jul 13, 2017
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  9. Babaganoosh

    Babaganoosh

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    I agree when it comes to the 4 mix engines
     
    Babaganoosh, Jul 14, 2017
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  10. MasterMech

    MasterMech The Mechanical Moderator

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    It's highly dependent on the oil you use, but going from 50:1 to 40:1 often results in cleaner internals. I've run AMSOIL Sabre Pro, Dominator, and TruFuel (all at 40:1) through both of my 4-mix engines with no trouble. Proper carb tuning and ignition system performance will go a long ways to prevent carbon issues. With a 4-mix, throttle response should be instant and strong, with a very clean, staccato exhaust note while running under load.
     
    MasterMech, Jul 15, 2017
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  11. MrWhoopee

    MrWhoopee

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    I had not heard of the 4-mix engine before. Pray tell, if it still requires mixed fuel, what is the advantage?
     
    MrWhoopee, Jul 15, 2017
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  12. TurboDiesel

    TurboDiesel

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    Less emissions =Meeting EPA requirements... more torque...better fuel efficiency
    The 4 mix doesn't have a oil sump and oil pump/feed system for lubrication (so you still need the mixed gas) which saves on weight and moving parts
     
    TurboDiesel, Jul 15, 2017
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  13. MasterMech

    MasterMech The Mechanical Moderator

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    Mixed fuel IS the advantage. Unlike other mini four-strokes, it doesn't have separate fluids to maintain, and lubricates in any position equally well.
     
    MasterMech, Jul 15, 2017
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  14. 94BULLITT

    94BULLITT

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    Torque
     
    94BULLITT, Jul 15, 2017
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  15. Ronaldo

    Ronaldo

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    Lighter weight than a sump 4 cycle, too.

    Sent from my SM-S320VL using Tapatalk
     
    Ronaldo, Jul 15, 2017
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  16. MrWhoopee

    MrWhoopee

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    When I asked about the advantage, I meant advantage over 2-cycle. I believe the emissions are cleaner (though since it's still burning oil, I question how much), but it's going to be heavier than a 2-cycle and much more complicated.
     
    MrWhoopee, Jul 15, 2017
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  17. 94BULLITT

    94BULLITT

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    They are quiet too.
     
    94BULLITT, Jul 15, 2017
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  18. MasterMech

    MasterMech The Mechanical Moderator

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    The emissions issue with traditional two-strokes centers around raw fuel being discharged into the exhaust during the cylinder scavanging cycle. Valves and four-strokes eliminate this while also making the engines quieter and torquey. All of this comes at a penalty of slightly increased mechanical complexity, a bit of weight, and a lower top-end rev limit. (Usually about 11k).

    In the Kombi type powerheads (split-boom, meant for attachments) these engines are notably good at cultivating and power sweeping in addition to being little monsters with the brush cutter and trimmer heads.

    With the backpack blowers, they have great throttle control and response throughout their rpm range, drink far less fuel than a traditional 2 stroke and are usually noticeably quieter given a certain output level.
     
    MasterMech, Jul 15, 2017
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  19. Kg461

    Kg461

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    Thats the way I see it also. The more oil u use the less likely it will combust completely which will stay wet and wash the motor instead of making a byproduct of full combustion, carbon?
     
    Last edited: Aug 4, 2017
    Kg461, Aug 4, 2017
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  20. cus_deluxe

    cus_deluxe

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    I like the 4-mix engine for trimmers etc..but in my experience its just not soemthing that holds up for long periods of WOT use. Ive worked with br600's for years at previous places of employment and they just dont hold up. Valves and seats and weak little plastic bits wear out and then your stuck with a $500 blower that you got 100 hours out of and will cost you $500 to rebuild. Ill take a redmax blower all day over a 4-mix blower. But for other applications they are actually very nice to use.
     
    cus_deluxe, Aug 4, 2017
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