New CS352--tuning and muffler mod advise

[Ratman]

I measure the petrol:oil to be between 45:1 and 50:1 on my mix as I find a number of saws come in with no significant reason to seize and can only put it down to slight over revving, slight mistake in mixing oil and perhaps a tiny air leak so a number of very insignificant issues making a big issue. My thinking is that a slight over egging on oil will help keep an engine protected more than perhaps making a slight mistake on the mix and risking seize.
I wonder how accurate many mixes people use actually are!

I used to use one shots in to 5L containers, i’m now on stihl green super with measuring dose on container in to a 1L mix bottle, as to keep my petrol oil mixes fresher as i dont use things mega often and to cut down on waste too.
I’m only a messer tho as you already know ?

[Sawchip]

24 minutes ago, spudulike said:

I measure the petrol:oil to be between 45:1 and 50:1 on my mix as I find a number of saws come in with no significant reason to seize and can only put it down to slight over revving, slight mistake in mixing oil and perhaps a tiny air leak so a number of very insignificant issues making a big issue. My thinking is that a slight over egging on oil will help keep an engine protected more than perhaps making a slight mistake on the mix and risking seize.

I wonder how accurate many mixes people use actually are!

On that point , I went to the trouble in testing a few of the 1 ltr mixing bottles commonly used by some of my customers !! ...worst was 16% out in favour of "more"  than 1 ltr of fuel in its measured amount .  

Edited March 8, 2019 by Sawchip

[Echo]

2 hours ago, Ratman said:

Over oiling (imo) would not help ring / piston to seal better but to eventually aid in glazing the bore resulting in poor performance, sticking rings (from emulsified oil/carbon)

 

To increase oil amount would mean increasing air/fuel ratios to compensate and keep up with performance??? I’m not following

I say if recommendations are 25:1 30:1 50:1 whatever.... then live by it but just use the highest quality oils available to aid it. ?‍♂️

 

Over oiling is not the answer, there have been studies done that determine the amount of oil an engine needs to lubricate its innards, when this figure is known, it must be provided, and in a chainsaw engine it is mixed in with the fuel, those who calculate this amount of oil also know how long it takes for an engine starting from cold to saturate all the bearings and coat the cylinder wall, at which point your engine is ready to be revved in anger, doing so sooner can cause damage from lack of oil.

 

So once the oil requirement is determined then the fueling can be calculated, two separate issues, but both are linked in that both mediums, oil to lubricate and fuel to power the engine come mixed, no one guessed these figures, for oil surface area, crank case pressure and mechanical aids such as the crank throwing oil and oil viscosity are all taken into account. viscosity does not matter in synthetic oil, as it is electrically attracted to the surfaces of the engine, designed to be so, it creeps into the microscopic pours of the metal, where the dino oils have to create a film between the moving parts and plays a very big role in this. Is Saber pro not semi synthetic, the best of both worlds, there seems to be a lot more to how oil does it job than may be immediately obvious.

I wish I knew more about it.

I took many engines apart that burned almost as much oil as fuel, and they were not glazed, just oily, oil in this quantity will stick rings and cause trouble, but if I had to chose between oil and soot, oil it would be, soot is like grit in your engine, and will destroy it in no time, oil can be cleaned off, which happens in race engines, it has to happen because they depend on a liberal dose of oil to keep the engine from ceasing up from the heat generated under high speed and power conditions.

In any event, when the fuel and oil are pulled into the two stroke, the fuel begins to separate as its heated and becomes lighter leaving the most of the oil in the lower end where it is needed, so not all the oil in the mix makes it above the piston. There is even a compression ratio calculated to assist in both fueling and oiling for the crank case as the piston moves down, this plays a part in the separation of the oil and fuel, as well as sending the charge up through the ports.

Edited March 9, 2019 by Echo

[Echo]

1 hour ago, Sawchip said:

On that point , I went to the trouble in testing a few of the 1 ltr mixing bottles commonly used by some of my customers !! ...worst was 16% out in favour of "more"  than 1 ltr of fuel in its measured amount .  

Yes, unfortunately there is discrepancies in the quantity contained in those mix bottles, that is why I measure mine from a larger bottle just to be sure. but there are a lot of factors in play at any one time, oil ratio is only one part of it, so its best to pick a mix ratio that you think will provide enough oil to lube and fuel to burn, heavy loaded saws need more oil and indeed more fuel helps cool them too as opposed to letting them go lean. the oil type, synthetic, dino, a mix of both as well as any other additives in the oil need to be considered, as these additives can cause problems if higher volumes of oil are mixed with the fuel, this is why there are so many oils out there, some more specific and limited than others, and the purpose it was designed for needs to be matched to the job at hand and the prevailing conditions.

[Echo]

2 hours ago, Ratman said:

Over oiling (imo) would not help ring / piston to seal better but to eventually aid in glazing the bore resulting in poor performance, sticking rings (from emulsified oil/carbon)

 

To increase oil amount would mean increasing air/fuel ratios to compensate and keep up with performance??? I’m not following

I say if recommendations are 25:1 30:1 50:1 whatever.... then live by it but just use the highest quality oils available to aid it. ?‍♂️

 

Glazing has more to do with too much heat in your cylinder and burning bad fuel, corn oil and such, and with the well machined surfaces we now have in nearly all engines, oil plays way less of a part in sealing the ring and piston, and with certain designs of rings, which are pushed out against the cylinder wall by the same pressure acting on the top of the piston, oil plays very little part in sealing, but is under more pressure to lube.

[lurkalot]

3 hours ago, spudulike said:

So are we saying say a 10:1 mix will make an engine over rev and seize being lean...I would propose it would smoke, run with poor performance and foul the plug....wouldn't it? I don't get it and not having a go, just don't see the logic!

No, I never mentioned 10:1 that would be rather foolish.  I said the difference between 50:1 and 32:1 with the same carb setting.   A general comment on a forum suggesting that adding extra oil to you mix for protection could result in problems,  which is why the manufacturer has recommended ratios.  But then we all know better than the people who make actually the stuff.

[Echo]

3 hours ago, spudulike said:

So are we saying say a 10:1 mix will make an engine over rev and seize being lean...I would propose it would smoke, run with poor performance and foul the plug....wouldn't it? I don't get it and not having a go, just don't see the logic!

Yes, more oil in your mix leans it,  the engine would get dangerously hot, so you need to adjust your carb to restore the balance. 18 to 1 is apparently where things get out of shape and  the amount of fuel you would need to run rich enough would not burn clean or in time, if it made it to above the cylinder, there would be all sorts of trouble with it burning.

Edited March 9, 2019 by Echo

[spudulike]

6 hours ago, lurkalot said:

No, I never mentioned 10:1 that would be rather foolish.  I said the difference between 50:1 and 32:1 with the same carb setting.   A general comment on a forum suggesting that adding extra oil to you mix for protection could result in problems,  which is why the manufacturer has recommended ratios.  But then we all know better than the people who make actually the stuff.

There are two trains of thought on the forum, extra oil and bang on manufacturers recommendation. My take on the manufacturers recommendation is that it will  probably adhere to EPA laws so will take in to consideration the pollution over oiling may cause rather than only considering what is best for the engine and providing a safety margin.

My 10:1 ratio was moving the mix to one you would never use, one so radical, it would have an obvious effect and I don't see a saw over revving on this mix - that may be another test I guess.

I have seen home owners saws come in with probably 25:1 in them, certainly not mixed at 50:1 and they don't rev and smoke like mad, it is just what they do and put that down to the oil fouling the plug and causing the plug not to ignite the mix on every stroke - four stroking. It is just what I have found, never seen any damage bar oily deposits and a bit of extra carbon, never seized and the plug was never white or grey....no death ash on it!

[spudulike]

Forgot to answer the original OPs question. I usually either bypass the cat or take it out depending on ease of modifying it.

On the L screw, most of the plug colour comes from flat out running. The L screw gives fuel for idle and around 1/3 throttle so effects pickup off idle and then hands over to the H speed check valve.

The L screw would normally be wound in to where the revs increase, a bit more to the point the saw is stalling and then out again, past the high revs part and then around 1/4 turn more. On most saws, the engine note changes from being rhythmical and consistent to getting slightly uneven and noticeably shaking a little more on its AV. This is my sweet spot! If the L screw is too far in, you will lack throttle response and starting will be difficult. Too far out and the saw will tend to die after a long cut when it falls back to idle.

That is what I have found anyway. Echo saws can be a bit finniky on the carb adjustment - the small ones being a right sod on occasions!

[wyk]

At a mix ratio of 32:1 vs 50:1, you have a difference of 1.125% more oil in the fuel mix - 3.125% VS 2%. 1.125% less petrol is not going to cause your engine to over heat or seize. However, the over all amount of oil that enters the engine at 32:1 is over half again more vs 50:1. So, at 32:1 VS 50:1 you risk an air/fuel ratio compromise of about 1% in order to get at least another 50% more lubrication in to the engine(but you really don't, as some of the oil makes it to combustion) - which is about 14.52:1 air to fuel VS what is the agreed upon 14.7:1 as the optimum fuel/air ratio for most petrol motors - assuming you do not tune your engine for your mix, and you go from 50:1 to 32:1. Autotune and mtronic (and you, if you know what you're doing) will tune this out as you tune for RPM or 'four stroking' and idle, which is a result of the air to fuel mixture, not the oil to fuel mixture. But, as is obvious, even if you do not touch your carb controls, chances are your mixture will be more affected by a change in weather than a change in your mix unless, as Steve has stated, you start to go down to crazy ratios.

 

At the end of the day it is called mix for a reason. The oil is now part of the fuel, not a separate entity as it is metered in to the saw. Not all of the oil will shear from the fuel as it goes through the engine - only part of it does - otherwise your saw would pour oil from every orifice after a few days of hard use. Much of it is burned(which is obvious if you look at the emissions tables on 2 strokes VS about anything else aside from diesels).

 

If you want to avoid seizing, carbon build up, etc etc - simply use a good high-quality fully synthetic oil designed for air-cooled non-marine application two strokes at a decent ratio, and make sure your engine is tuned properly.

Edited March 9, 2019 by wyk