New 880

[spudulike]

9 hours ago, Baldbloke said:

 

 

I was always told that adding extra 2T oil is not so good because it alters the fuel/air ratios. A lean fuel mix can make the top end run hotter.
Also that on and off the throttle let’s things bed in better, along with light initial workloads.

 

Man....this is like Groundhog day, who is this fella with the info? Dumb or Dumber

Sure, adding more oil makes the saw run leaner but not like the conventional fuel to air mix that can make a saw overheat. Your mix will still be the same fuel to air, it is the fuel to oil ratio that changes and this wont overheat a saw.

Proof - try a 25:1 mix in your saw, it won't rev well, will smoke like a chain smoking tart and wont get anywhere near overheating!!!

[Rough Hewn]

Hi Con fuck I totaly remember that as from my 2 stroke days , so anyway fouled it up this afternoon when the bloody rain stopped, and free handed a small walnut chog I had kicking around in the yard , totaly chuffed ace new saw , after the year I had last year good way to start this one , now I need 4 ft bar and chain , as I got a call today to go and Mill 2 , oak butts 3 ft wide and 10 ft long , it will be tough on my ankle but hey got to get on 
Thanks for all your comments  Mark

Might have an old 48" .404 "spare" chain if you want?
Haven't got a 48" bar but bizarrely I do have a brand new 17" 3002 mount bar
Could mill some 12" stuff?[emoji848]
Free to a good home?
[emoji106]

[Baldbloke]

20 minutes ago, spudulike said:

Man....this is like Groundhog day, who is this fella with the info? Dumb or Dumber

Sure, adding more oil makes the saw run leaner but not like the conventional fuel to air mix that can make a saw overheat. Your mix will still be the same fuel to air, it is the fuel to oil ratio that changes and this wont overheat a saw.

Proof - try a 25:1 mix in your saw, it won't rev well, will smoke like a chain smoking tart and wont get anywhere near overheating!!!

I’m no expert on saws but I used to do a few rebuilds on the old TZ and RG race bikes in the late 70/80s. I realise the oil wasn’t fully or part synthetic in those days and it was more common to run 2Ts at nearer 25:1 then. There was a guy who experienced as many nip ups and seizures as all the others I knew combined. It turned out he was overoiling his mixes thinking he was being kind to his motor. 

As a mix, only so much oil and fuel is able to be delivered through the main jet. Overoiling maybe great for the bottom end bearings and small end but that extra “teaspoon of oil” to a tankful of chainsaw oil is a significant reduction of fuel to air mix. You yourself admit it can lean off the mix because of this, so why do this to a new saw?  I would suggest that the extra oil is counterproductive and even if it doesn’t make the top end run hotter, it will add coke to the plug. 

Surely if Sthil thought it necessary to add extra oil into the mix they would say so? Dumb or Dumber with your response?

[spudulike]

You misread my post, I was saying that we usually talk about "LEAN" meaning more AIR to FUEL MIX entering the engine.

I was stating that adding more oil reduces the amount of FUEL and increases the amount of OIL in the total engine charge and not the amount of AIR entering the engine thinking the fuel mix flow wouldn't be effected.

It is damn difficult to say if the check valve is effected in any way with a greater amount of oil in the fuel thus reducing the fuel mix coming through it. I would have thought the flow and viscosity of such a fluid mix would be negligible - at 25:1, it would be far more having a greater amount of oil in it and would also think the oil was more viscous in those days.

The TZ would have slide carbs, am guessing Mikuni from my past and these would probably react in a different way to a chainsaw carb - slide, needle and jet rather than check valve as on a saw.

Good to know you have a decent background, we are never going to prove the flow characteristics without a lengthy trial but my take when most people come out with this statement think somehow that the saw will be taking in more air because they are adding more oil!

I guess it would be interesting to see if a 50:1 mix makes the cylinder hotter than a 40:1 mix or vice versa - pretty easy with a laser heat gun. Something to do on a quiet day!

[Baldbloke]

You misread my post, I was saying that we usually talk about "LEAN" meaning more AIR to FUEL MIX entering the engine.
I was stating that adding more oil reduces the amount of FUEL and increases the amount of OIL in the total engine charge and not the amount of AIR entering the engine thinking the fuel mix flow wouldn't be effected.
It is damn difficult to say if the check valve is effected in any way with a greater amount of oil in the fuel thus reducing the fuel mix coming through it. I would have thought the flow and viscosity of such a fluid mix would be negligible - at 25:1, it would be far more having a greater amount of oil in it and would also think the oil was more viscous in those days.
The TZ would have slide carbs, am guessing Mikuni from my past and these would probably react in a different way to a chainsaw carb - slide, needle and jet rather than check valve as on a saw.
Good to know you have a decent background, we are never going to prove the flow characteristics without a lengthy trial but my take when most people come out with this statement think somehow that the saw will be taking in more air because they are adding more oil!
I guess it would be interesting to see if a 50:1 mix makes the cylinder hotter than a 40:1 mix or vice versa - pretty easy with a laser heat gun. Something to do on a quiet day!

Sorry, but you yourself said that the fuel air mix will be unaffected. That is incorrect when a portion of that pre-mixed fuel compromises more than recommenced amount of 2 T oil. You too will be well aware that the fuel is acknowledged as an essential part of the cooling part of the cycle prior to combustion and the oil is for lubrication.
So, by adding more oil YOU ARE reducing the fuel to air ratio as it is a pre-mix, and has to travel through an exactly predetermined size of jet before entering the crankcase prior to the cylinder.
Over-oiling while good for lubrication leans off the mix, so my suggestion was that it can be counterproductive by raising cylinder temperature. A rise over and above the norm, especially in a new and tight piston to bore interface is not what most engines need.

Having never had to bother to fully rebuild a saw (just plenty of 2 and 4 T motor cycles and performance car engines/boxes) I will defer to your acknowledged experience on saws. However, I believe your comment that I’m Dumb or Dumber was unnecessary considering you know little of my background.

[Toad]

Stoichiometric air to fuel ratio is 14.7:1

 

50:1 fuel oil mix is 2% oil, 33:1 Is 3% therefore a 1% decrease in actual fuel. 

 

That would take a saw running at stoic (unlikely I know) from 14.7:1 to 14.7:0.99. The actual difference in the air to fuel is tiny. I'm not sure many of us will be that accurate when mixing fuel anyway.

[spudulike]

I apologise for the dumb and dumber bit as obviously your comments come from a background of bike racing rather than the misguided comments to be found on the internet as I thought was the case and is generally so with many.

 

When I talk about the fuel, I am talking about a mix of oil and petrol being fuel and not petrol by itself. What I was saying was that if you had 100mg of fuel (Oil + Petrol) going through an engine in a minute then if you upped the oil and decreased the fuel, you would still have that same amount of "Fuel"  going in to the engine but you would have more oil and less fuel and wouldn't effect the volume of air so describing it as LEANING the fuel air mix was a bit misleading.

I think you are thinking I am calling fuel just petrol and I am clearly not, fuel to me is what you stick in the fuel tank and not just the petrol content as I think you are taking it to be......I hope so as I want to get some sleep tonight!

 

Anyway, perhaps one day I will have to try two different fuel mixes in the same saw and measure the temp of the top end and see what happens, at least it will prove what is fact and I learn every day.

 

[spudulike]

14 minutes ago, Toad said:

Stoichiometric air to fuel ratio is 14.7:1

 

50:1 fuel oil mix is 2% oil, 33:1 Is 3% therefore a 1% decrease in actual fuel. 

 

That would take a saw running at stoic (unlikely I know) from 14.7:1 to 14.7:0.99. The actual difference in the air to fuel is tiny. I'm not sure many of us will be that accurate when mixing fuel anyway.

Agree and read my last post on my comments about my definition that fuel is "what goes in to the fuel tank" and not just petrol!

Think we have been dancing round different terms.

Thanks and goodnight.

[Baldbloke]

12 hours ago, spudulike said:

I apologise for the dumb and dumber bit as obviously your comments come from a background of bike racing rather than the misguided comments to be found on the internet as I thought was the case and is generally so with many.

 

When I talk about the fuel, I am talking about a mix of oil and petrol being fuel and not petrol by itself. What I was saying was that if you had 100mg of fuel (Oil + Petrol) going through an engine in a minute then if you upped the oil and decreased the fuel, you would still have that same amount of "Fuel"  going in to the engine but you would have more oil and less fuel and wouldn't effect the volume of air so describing it as LEANING the fuel air mix was a bit misleading.

I think you are thinking I am calling fuel just petrol and I am clearly not, fuel to me is what you stick in the fuel tank and not just the petrol content as I think you are taking it to be......I hope so as I want to get some sleep tonight!

 

Anyway, perhaps one day I will have to try two different fuel mixes in the same saw and measure the temp of the top end and see what happens, at least it will prove what is fact and I learn every day.

 

No problem. I probably wasn't too clear about which posts I was actually referring to.

 

Various previous posts had suggested that rich oil mixes as well as running a few tankfuls through a new saw at tickover might be good for a saw as a method for breaking them in. I personally don't believe that adding extra oil or running them at tickover for prolonged periods is beneficial. With running in 2 stroke bike engines we believed in being on and off the throttle (so that all the components settled in) and building up on the load/work fairly quickly. We also avoiding coasting off throttle for prolonged periods. We were forever whipping out plugs in those days, as this before unleaded fuels, and it gave a good idea on correct jet choice.

However, someone else helpfully provided some figures about mix proportions against volume percentages which suggested that there is safe leeway.

Carb jets in the name of efficiency are tiny, so there is something else to consider. Over oiling does change the viscosity of the fuel, so atomisation is poorer. Combine that with not running a high performance 2T motor at the designed full revs (or leaving a new saw ticking over for a few tanks strapped to a pallet as someone suggested) the droplet heavy mix entering the crankcase has a limited swirl effect and an inferior mist before it has the chance to enter the combustion chamber. Additionally, as the burn would be inefficient (because a saw is not designed to run in this manner) it is much more likely to leave unburnt oil deposits as coke on the plug and the exhaust port. Just where you don't want it.  

 

 

  

 

 

 

 

 

 

[Mark Bolam]

So.

Just run it flat out, then?