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Fuel mix preferences

Started by thutch85, February 01, 2018, 10:47:52 PM

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Al_Smith

 :D They just carry on like a chainsaw is a vintage Roll-Royce or something .Run aviation gas,high octane rocket fuel ,oil at 100 to 1 ratios and so much stuff you could over load this server .Of course as is my nature my job is to heckle which I'm very good at .Truth be known I could care less what anybody does with their saws . 8)

martyinmi

Quote from: John Mc on February 03, 2018, 04:16:35 PM
All octane does is prevent the spontaneous ignition of the fuel-air mixture as it is compressed.


Spontaneous ignition...or auto ignition?  ;D
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John Mc

Quote from: martyinmi on February 08, 2018, 09:38:35 PM
Quote from: John Mc on February 03, 2018, 04:16:35 PM
All octane does is prevent the spontaneous ignition of the fuel-air mixture as it is compressed.

Spontaneous ignition...or auto ignition?  ;D

Took those words from a page explaining about Octane. They went further to explain that it would ignite from the compression alone, rather than needing a spark. (Now that you mention it, igniting from compression is not really "spontaneous")
If the only tool you have is a hammer, you tend to see every problem as a nail.   - Abraham Maslow

JohnW

John Mc, ignition from compression is still spontaneous combustion, according to the usual meaning of spontaneous combustion.  It's combustion, not according to the plan, or maybe combustion on its own timing, not by the spark plug.

John Mc

Quote from: JohnW on February 08, 2018, 10:35:09 PM
John Mc, ignition from compression is still spontaneous combustion, according to the usual meaning of spontaneous combustion.  It's combustion, not according to the plan, or maybe combustion on its own timing, not by the spark plug.

I'm aware that the term is normally used that way. My comment was more an observation that it is an odd use of the word. It is not really "spontaneous" by the common (non-automotive/gas engine) use of the word. You compressed the mixture, it caused the mix to heat up and ignite. Nothing really "spontaneous" about that, even though it is not the intended method of ignition.
If the only tool you have is a hammer, you tend to see every problem as a nail.   - Abraham Maslow

HolmenTree

My experiences in timbersports I've had "run away " saws.
Once had a Stihl 090 that I modified with high compression running a race fuel mixture.
After the last cut when I tried to shut it off it just kept going WOT. Pulled the spark plug boot off the plug it still kept screaming.
Ended up holding the throttle wide open until it cooled down enough to stop.
Red hot piece of carbon or something kept it going
Making a living with a saw since age 16.

sablatnic

Same happened to me with a heavily modified Partner.
It just idled along with ignition turned off,  while I had time to unscrew the top cover and pull the wire off the plug. Kept idling without the wire for several minutes, till it had cooled off.
At the time we guessed that the spark plug or a piece of carbon kept warm enough to keep it running.

Al_Smith

Quote from: martyinmi on February 08, 2018, 09:38:35 PM
Quote from: John Mc on February 03, 2018, 04:16:35 PM
All octane does is prevent the spontaneous ignition of the fuel-air mixture as it is compressed.


Spontaneous ignition...or auto ignition?  ;D
Oh goody Marty showed up . 8)

Al_Smith

It wasn't a chainsaw but I once owned a 1973 Olds Toronado that would diesel enough you could drive it a city block before it would stop .455 cubic inch monster that loved gasoline .It was supposed to have a solenoid on the carb throttle plate to shut it completely off to prevent that .Evidently it didn't work so well .Got real stinky dieseling on gasoline,phew .
Now that engine was in the days of"low lead" not no lead .So perhaps the formulation of that stuff wasn't so good .It ran pretty good on Sunoco 260 though .

thedoublejranch

Quote from: PNWRusty on February 03, 2018, 02:02:46 PM
I just run what the manufacturer of the engine recommends. Works for me but I've only been using a chainsaw for the last 42 years so maybe I'm being foolish.

42 years ago, be hard pressed to find gas with alcohol in it, now its almost a normal thing. You have to actively search for alcohol free fuel now and the sources are very limited. That fuel creates havoc if you have saws that set with no use for a few months or more. If your saws run all year long, its a non issue as you stated.
To find alcohol free pump gas, try http://pure-gas.org
The Double J Ranch & Timber Farm.
Member "NWOA" National Woodland Owners Association"

Enderslbz

Quote from: Woodcutter_Mo on February 02, 2018, 11:18:28 PM
I've heared of scented fuel additives for the RC cars that run on the nitro methane stuff, never for a chainsaw though  ???

Never tried an octane booster in the 2 strokes. I may try it in one of my older saws and see what it does.

OMG I love that smell, why would you ever want to cover it up  ???
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JohnW

I have a couple octane questions, if I can borrow the post for a minute.  I suppose if the octane is too low, and you have run on when you turn your saw off, then the saw is probably also firing too early before top dead center, also, resulting in power loss.  Is that right?  I've been using 100LL in my saws (310, 372, and 395) but as people have pointed out, low lead aint no lead.  I should probably switch.  The 92 octane 50:1 premix stuff looks good.  On switching, I probably need to get my saws retuned, right?

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