mixing ratios for 2 stroke chainsaws

[bwalker]

To add to the answers of oil ratios, I use 25:1 100LL/Maxima K2 in my 3120xp and 30:1 in my smaller stihls.
I've had to switch carbs in the 3120xp to a WB37 with some modifications so that I can adjust the high-speed circuit. WB37 doesn't come with a choke, so use a fabbed linkage to prime the diaphragm. Works really well. Operating at about 1000'-1500' msl at density-altitudes of 0'-5000', depending on weather conditions, so careful carb-tuning each day is a prerequisite to a happy engine. Pistons always appear bright and clean, top and bottom... obviously because it's running cool. I've done some tame porting mods to the 3120xp -- trimmed the base so compression is up to around a true 10:1; squish is tight at around 0.30mm, lower transfers opened and radiused for good flow; transfer tunnels smoothed and polished (kinda). Merely widened the exhaust port, upper transfers, and intake poer a bit. Unlimited coil retarded by 12 degrees makes for easy starts and tons of power over 8500 rpm. Fabbed custom exhaust. Lightened and flowed piston; coned piston-pin ends. Balanced crank/rod/piston assembly. Try to keep her below 12,000 rpm. Runs like a raped ape, but super-smooth. A real pleasure to handle.

K2 is good oil.

 

[North by Northwest]

To add to the answers of oil ratios, I use 25:1 100LL/Maxima K2 in my 3120xp and 30:1 in my smaller stihls.
I've had to switch carbs in the 3120xp to a WB37 with some modifications so that I can adjust the high-speed circuit. WB37 doesn't come with a choke, so use a fabbed linkage to prime the diaphragm. Works really well. Operating at about 1000'-4000' msl at density-altitudes of (-)100' through (+)6000', depending on weather conditions, so careful carb-tuning each day is a prerequisite to a happy engine. Pistons always appear bright and clean, top and bottom... obviously because it's running cool. I've done some tame porting mods to the 3120xp -- trimmed the base so compression is up to around a true 10:1; squish is tight at around 0.30mm, lower transfers opened and radiused for good flow; transfer tunnels smoothed and polished (kinda). Merely widened the exhaust port, upper transfers, and intake port a bit. Unlimited coil retarded by 12 degrees makes for easy starts and tons of power over 8500 rpm. Fabbed custom exhaust. Lightened and flowed piston; coned piston-pin ends. Balanced crank/rod/piston assembly. Try to keep her below 12,000 rpm. Runs like a raped ape, but super-smooth. A real pleasure to handle.

Raduising your transfers really improves laminiar flow with less turbulence , which inhances scavenging & better overall power delivery . What was your intake & exhaust numbers & duration & degree of blowdown efficiency !

 

[ZeroJunk]

Will some oils actually dry up over time? I just pulled apart a junkyard Husqvarna 50 that had a very nice oem piston/cylinder in it. The crankshaft was very difficult to move and I thought the bearings were shot. On a hunch I oiled them up and now they move freely. Oiling the seals seemed to make no difference.
This is a cause for concern if I was going to store a saw for any length of time, I'm now thinking fogging will be mandatory.
It seems so little oil was left in the crank of that saw, yet there is no scoring and it would be fine with just a new ring. Or perhaps this is carbon from blow by that has hardened over time and the oil loosened it up? It did have some carbon stains in the crankcase.
Maybe that extra bit of oil at 40:1 vs 50:1 will have another benefit besides reduced engine wear, more oil in the crankcase for long term storage.

I bought the 2101XP in my avatar as being locked up. I took a squirt can of mix and sent a shot down the spark plug hole, pulled it over a few times, put the plug in and it cranked right up. About as close to new as you can get.

So, I don't see that as being a bad scheme for a sitting saw.

 

[bwalker]

I bought the 2101XP in my avatar as being locked up. I took a squirt can of mix and sent a shot down the spark plug hole, pulled it over a few times, put the plug in and it cranked right up. About as close to new as you can get.

So, I don't see that as being a bad scheme for a sitting saw.

Gasoline is a great solvent, so that's what probably broke your saw free. However mixed gas has nearly zero ability to lubricate. As such its better to fog them or have ample residual oil.

 

[ZeroJunk]

Gasoline is a great solvent, so that's what probably broke your saw free. However mixed gas has nearly zero ability to lubricate. As such its better to fog them or have ample residual oil.

That's curious opinion since you are saying in another breath that lack of mixed gas is taking out your bearings.

 

[OM617YOTA]

.... That's not what he's said. FFS dude.

 

[bwalker]

That's curious opinion since you are saying in another breath that lack of mixed gas is taking out your bearings.

You only think that because your not using your brain...
When pre mix enters the crankcase of a running two cycle the fuel flashes to vapor and the oil is deposited on the rotating parts...for the second time.
Pre mixed fuel has nearly zero lubricating ability. Only once the oil drops out of suspension and coats the internals does any lubrication take place.

 

[MacAttack]

You're suggesting the oil doesn't make it's way through the transfer ports and into the combustion chamber? Or that some portion of the oil is deposited in the crankcase?

 

[KASH]

Well Zero Junk you must have the mix ratio down pat you unsiezed the saw started her up and she still runs like a charm.Excellent job no pun intended.
Kash

 

[bwalker]

You're suggesting the oil doesn't make it's way through the transfer ports and into the combustion chamber? Or that some portion of the oil is deposited in the crankcase?

In a properly tuned engine the majority of the oil is deposited in the crankcase and migrates from there.
If the fuel doesn't vaporize it doesn't burn well, which is why two strokes when cold smoke and require alot of choke to start.
This isn't earth shattering stuff..

 

[ZeroJunk]

Well Zero Junk you must have the mix ratio down pat you unsiezed the saw started her up and she still runs like a charm.Excellent job no pun intended.
Kash

No, it was never seized to start with. Those things are a ***** to pull when being used every day, much less when they are dry.

 

[Hman1024]

Fuel does a lot in the way of cooling. Essentially you need enough oil in your fuel to give good lubrication, & enough fuel to slightly exceed the "optimum" air fuel ratio. The additional fuel helps cooling & brings rpm down to mechanical design.
Different oils burn differently

J D brought up many valid points on the topic. Having grown up on motocross bikes was my introduction to 2 strokes that then turned into chainsaw habits. Fine balance between enough lubrication and excess. In the end each machine is going to act uniquely. Let's not for the other two components that make up that power/protection equation, air flow and fuel quality. If you want to go by the science, get a digital tachometer (can sense changes that ears can't hear) and tune for specific saw (equipment), fuel, oil, any mods, your type of saw usage, firewood, timber or sawmill application.

If interested, with the attachment, you can geek out on on the science behind two strokes and how they work in relation to these attributes but also gets into exhaust porting, timing and about anything you can dream of.

 

[MacAttack]

In a properly tuned engine the majority of the oil is deposited in the crankcase and migrates from there.
If the fuel doesn't vaporize it doesn't burn well, which is why two strokes when cold smoke and require alot of choke to start.
This isn't earth shattering stuff..

I'm always looking to learn something new, you've posted a lot of knowledgeable info but I'll have to agree to disagree on this one. Maybe there's something you can cite in a link that I can check out?
My understanding was always that the smoke on startup is due to unburned oil / fuel due to a cold engine being inefficient, the same as a cold diesel engine or a 4-cycle gas engine with a lot of choke smoking at startup. Unburned fuel = smoke. Once it's warmed up and burning efficiently the smoke subsides.
I can't buy into the idea that the oil drops out of the mix, obviously SOME oil lubricates the bottom end, that's it's job! But a freshly rebuilt 2 stroke smokes immediately because of the oil burning out of the combustion chamber.
But ...I love to learn something new, why am I wrong?

 

[ZeroJunk]

What I was talking about is the mix slicking up the cylinder walls. On saws that have been sitting a long time you can feel it smooth up almost on the first pull.
The oil mixed with gas is part of it.

 

[sean donato]

I don't doubt you. There were complaints with larger displacement Husqvarnas going back at least a decade that I am pretty sure were single intake. And, guys were saying that 32 to 1 helped.

I still have some questions. Of that percentage of oil wasted out the exhaust, how much could have been stacked on bearings anyway? I don't know. How much oil can be attached to the surface of a bearing ? I don't know. At some point it is like pouring water on the hood of your car./

I was told that the reason why older saws had a heavier mix in addition to the oil not being as good was that the tolerances were sloppier. I don't know.

My thinking is simply that the engineers who blend the oil and design the saws do.

But, it would be foolish to think nothing slips through the cracks as well.

I have one tree service customer that has three of the non Mtronic 362's that have that dual intake carb. He works them hard. Only problem he has had is his men manage to get that stupid piece of linkage out of the slot somehow. You couldn't do it trying. And, I took some 1708 fiberglass and epoxy and repaired a broken rear handle, Probably 5 years ago and still holding fine. I have no idea what oil he runs, but he just gets regular ethanol at the gas station every day. Hell, he's still using an 044 that has who knows how many hours on it. Think I replaced the carb, fuel line, and tank vent once.

Anyhow, I work on a lot of MS201T's for some reason. Big saws are rare. I rebuilt a MS462C that hung a skirt a few weeks ago. But, mostly home owner saws. And, blowers, weedeaters, trimmers, and pole saws forever.

If there is a logger in the bunch I don't know them.

Up untill last year someone husqy recommended 33 to 1 in any saw over 60cc. Sometime last year they moved that to over 75cc. Which I think was a mistake but for whatever reason that's their reccomendations.

 

[camel2019]

That's curious opinion since you are saying in another breath that lack of mixed gas is taking out your bearings.

There’s a huge difference between liquid gasoline and the vaporized mix that comes in through the a carb.

 

[MacAttack]

So... I've found similar accounts on the web " the oil suspended in premix deposits in the crankcase to replace oil migrating to the combustion chamber" or similar, interesting.
I'd love to see something in a controlled experiment to show this.

 

[camel2019]

What I was talking about is the mix slicking up the cylinder walls. On saws that have been sitting a long time you can feel it smooth up almost on the first pull.
The oil mixed with gas is part of it.

Like said earlier in this thread liquid fuel is basically a solvent in the past I have used it as such.

 

[bwalker]

I'm always looking to learn something new, you've posted a lot of knowledgeable info but I'll have to agree to disagree on this one. Maybe there's something you can cite in a link that I can check out?
My understanding was always that the smoke on startup is due to unburned oil / fuel due to a cold engine being inefficient, the same as a cold diesel engine or a 4-cycle gas engine with a lot of choke smoking at startup. Unburned fuel = smoke. Once it's warmed up and burning efficiently the smoke subsides.
I can't buy into the idea that the oil drops out of the mix, obviously SOME oil lubricates the bottom end, that's it's job! But a freshly rebuilt 2 stroke smokes immediately because of the oil burning out of the combustion chamber.
But ...I love to learn something new, why am I wrong?

The smoke at start up is because of unburnt fuel. Fuel that isn't in a vapor form can't burn..
You can disagree but this is very basic stuff.
And the oil has to drop out of suspension to lubricate.
It's also why you find oil in the crankcase of a non running engine but not fuel.

 

[bwalker]

So... I've found similar accounts on the web " the oil suspended in premix deposits in the crankcase to replace oil migrating to the combustion chamber" or similar, interesting.
I'd love to see something in a controlled experiment to show this.

That's how it works.....