mixing ratios for 2 stroke chainsaws

[bwalker]

Could have. Mix did the trick just fine. Saying it has no lubricating properties when I can feel it immediately pulling it is some typical forum BS. I had an 036 that hadn't been run in years, and the owner was saying the bearings or who knows what else was out of it. I squirted some mix down the plug hole and had it running in 30 seconds. He wanted to know what I had done to it , and I said basically nothing.

I suspect if you would actually do some of this instead of being this cycles forum know it all might help you get a better grasp of the real world of making things run.

PREMIX has zero lubricating properties! Get that through your thick skull.
I don't know it all, but clearly many here have a leg up on YOU.
I suspect you haven't done a whole lot of mechanic work, because you can't comprehend the basics..
My job is to get pieces of equipment running and to keep them running. Much more expensive than a 500 dollar dead simple chainsaw...

 

[Bob Hedgecutter]

Got to love an oil thread- usually about 2 pages in the original question is lost- lots of irrelevant information about 2 stroke motorcycles, followed by a pissing contest or three.
Kind of like passing a wreck involving a school bus and a semi trailer- you shouldn't stare, but it is hard not to.
For 75% of casual users and even members on here- pick an oil you like the look of- pick a ratio you can understand somewhere between 30:1 and 50:1, mix your fuel, tune the saw to your chosen mix, run the saw- if it dies- learn from it!

 

[Pioneer]

Carburetors convert the fuel into a very fine aerosol. When it enters the combustion chamber some of it gets turned into a true vapor as it hits the hot surfaces, some remains suspended in very fine droplets where they flash into vapor as the flame front reaches them after ignition. Some makes its way through without ever getting burnt, especially true in a cold, slow running, or both, engine.

The old v8s used a heat riser in the intake manifold to help promote better vaporization of the fuel mix at low RPM. This is why you found out that blocking off that riser gave you worse mileage.

Carburetors do a lousy job of atomization at low RPM. This is one of the reasons why we went to fuel injection, they do not rely on air velocity for this to happen. The smaller atomized droplets promote more complete burning and better fuel efficiency.

Many years ago I played around with the true vapor system in an old Toyota, where I preheated fuel to a complete vapor and then routed it to the engine. I used an air bleed valve to control the mixture, and used a heater box where I pumped hot antifreeze through to heat the fuel and then pumped the hot fuel onto a large surface area where air was drawn past to pick up the vapor.
One thing became immediately apparent, there was a marked improvement in low speed performance. You could put the car in fifth gear, bring it right down to 800 RPM and then hit full throttle. It would accelerate absolutely smoothly, where with the carburetor it would buck and spit until it hit a half decent RPM.
Fuel mileage came up somewhere around 10% in town, but I ultimately shelved the system because it could not supply enough vapor to get the car over 60 mph.

Another thing I learned is that our gasoline is a witches brew of different components and will turn into a brown sludge if you let the volatiles completely evaporate away from sitting at room temperature. You have to heat gasoline quite a bit to get all of them to vaporize. Naptha is a much cleaner fuel and quite a bit better suited for vaporization. The reason why we use it in camp stoves.
So, heat and rpm play an important role in carbureted engines when it comes to proper burning of the fuel mixture, factor in the oil mix ratio and oil type and you have another set of variables to contend with.

 

[KASH]

In November of 1979 I bought my Husky 162 se from Noro Saw .At this period in time and for years after the cutting of pulp wood by cut and skid was in its hey day with many company bush camps and many private contractors.Noro was the largest seller of Husky in North America.My brother and I both bought 162s and part of the deal was 2 chains and a case of Castroll 2 stroke oil.The two Swedes told us to mix it at 1 quart to 5 gallons I was reading the owners manual and pointed out that it said if you used Husky oil you could mix 50 to 1 but if you used any other oil it was 25 to1.The two guys chuckled and one said go ahead and mix it at 50to1 you will be back to buy another saw in a little while.
Kash

 

[Tomos770]

Carburetors convert the fuel into a very fine aerosol. When it enters the combustion chamber some of it gets turned into a true vapor as it hits the hot surfaces, some remains suspended in very fine droplets where they flash into vapor as the flame front reaches them after ignition. Some makes its way through without ever getting burnt, especially true in a cold, slow running, or both, engine.

The old v8s used a heat riser in the intake manifold to help promote better vaporization of the fuel mix at low RPM. This is why you found out that blocking off that riser gave you worse mileage.

Carburetors do a lousy job of atomization at low RPM. This is one of the reasons why we went to fuel injection, they do not rely on air velocity for this to happen. The smaller atomized droplets promote more complete burning and better fuel efficiency.

Many years ago I played around with the true vapor system in an old Toyota, where I preheated fuel to a complete vapor and then routed it to the engine. I used an air bleed valve to control the mixture, and used a heater box where I pumped hot antifreeze through to heat the fuel and then pumped the hot fuel onto a large surface area where air was drawn past to pick up the vapor.
One thing became immediately apparent, there was a marked improvement in low speed performance. You could put the car in fifth gear, bring it right down to 800 RPM and then hit full throttle. It would accelerate absolutely smoothly, where with the carburetor it would buck and spit until it hit a half decent RPM.
Fuel mileage came up somewhere around 10% in town, but I ultimately shelved the system because it could not supply enough vapor to get the car over 60 mph.

Another thing I learned is that our gasoline is a witches brew of different components and will turn into a brown sludge if you let the volatiles completely evaporate away from sitting at room temperature. You have to heat gasoline quite a bit to get all of them to vaporize. Naptha is a much cleaner fuel and quite a bit better suited for vaporization. The reason why we use it in camp stoves.
So, heat and rpm play an important role in carbureted engines when it comes to proper burning of the fuel mixture, factor in the oil mix ratio and oil type and you have another set of variables to contend with.

Slo-mo @6:32

 

[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.

I did not hear back on your numbers brother , however recently woods ported a quad port 357 xp . I ran with a conservative .018 squish , 141 duration & 13.5 deg. of blowdown & achieved a 500+ rpm gain over stock with a minor muffler mod & goobs of low & midrange torgue . The overall compression with the crank stuffers was pretty well unaffected + a couple of points . I still run 91 octane with Saber @ 44:1 . Very strong firewood saw. P.S. I usually use a 10 deg. raduis on all chamfers including the transfers .

 

[Hermio]

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.

Strictly speaking, the oil is not in suspension. It is in solution. When the gasoline evaporates, the oil remains.

 

[sawmill sam]

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.

well spoken sir! Best explanation I have ever heard.

 

[bwalker]

Strictly speaking, the oil is not in suspension. It is in solution. When the gasoline evaporates, the oil remains.

What ever. You know what I ment.

 

[bwalker]

Carburetors convert the fuel into a very fine aerosol. When it enters the combustion chamber some of it gets turned into a true vapor as it hits the hot surfaces, some remains suspended in very fine droplets where they flash into vapor as the flame front reaches them after ignition. Some makes its way through without ever getting burnt, especially true in a cold, slow running, or both, engine.

The old v8s used a heat riser in the intake manifold to help promote better vaporization of the fuel mix at low RPM. This is why you found out that blocking off that riser gave you worse mileage.

Carburetors do a lousy job of atomization at low RPM. This is one of the reasons why we went to fuel injection, they do not rely on air velocity for this to happen. The smaller atomized droplets promote more complete burning and better fuel efficiency.

Many years ago I played around with the true vapor system in an old Toyota, where I preheated fuel to a complete vapor and then routed it to the engine. I used an air bleed valve to control the mixture, and used a heater box where I pumped hot antifreeze through to heat the fuel and then pumped the hot fuel onto a large surface area where air was drawn past to pick up the vapor.
One thing became immediately apparent, there was a marked improvement in low speed performance. You could put the car in fifth gear, bring it right down to 800 RPM and then hit full throttle. It would accelerate absolutely smoothly, where with the carburetor it would buck and spit until it hit a half decent RPM.
Fuel mileage came up somewhere around 10% in town, but I ultimately shelved the system because it could not supply enough vapor to get the car over 60 mph.

Another thing I learned is that our gasoline is a witches brew of different components and will turn into a brown sludge if you let the volatiles completely evaporate away from sitting at room temperature. You have to heat gasoline quite a bit to get all of them to vaporize. Naptha is a much cleaner fuel and quite a bit better suited for vaporization. The reason why we use it in camp stoves.
So, heat and rpm play an important role in carbureted engines when it comes to proper burning of the fuel mixture, factor in the oil mix ratio and oil type and you have another set of variables to contend with.

Naptha has a higher boiling point than gasoline range components. As a results it doesnt vaporize as easily as gasoline.
Also keep in mind that what ever gasoline enters the combustion chamber in liquid form pulls heat from the combustion event, which energy that could be used to drive the piston down.
Car engines and especially old V8's have really long intake runners and easily vaporize most of the fuel admitted to the engine.
The portions of fuel passing through an engine uncombusted are what we call in the refining industry "heavies". They like wise sap power from the engine and will go through a two cycle with out changing phase or partially changing phase/coking, which is what causes much of the deposits seen in a two cycle.

 

[North by Northwest]

well spoken sir! Best explanation I have ever heard.

The turbulence within the crankcase due to the reciprocating mass's , enhances the oil filming capability incredibily !

 

[bwalker]

The turbulence within the crankcase due to the reciprocating mass's , enhances the oil filming capability incredibily !

That's one of the mechanisms that's moves the oil around.

 

[North by Northwest]

That's one of the mechanisms that's moves the oil a

That's one of the mechanisms that's moves the oil around.

Also , the natural rate of vaporization as the oil moves from the crankcase up through the transfers to be burnt or expelled out the exhaust port after wetting metal surfaces , to an extent when you drop rpms , there is a natural wiping action that allows oil to drip back down into the crank & bearing from the cylinder walls . Capillary action to a much lesser degree I imagine also . However , that's all I can further contribute brother on the oil migration potential , within a 2T Premix engine . P.S. Oil Injected systems also inject directly to the small & big end bearings or directly into the intake runner to be aspirated into the fuel charge , although not within saws that iam currently aware ?

 

[bwalker]

Also , the natural rate of vaporization as the oil moves from the crankcase up through the transfers to be burnt or expelled out the exhaust port after wetting metal surfaces , to an extent when you drop rpms , there is a natural wiping action that allows oil to drip back down into the crank & bearing from the cylinder walls . Capillary action to a much lesser degree I imagine also . However , that's all I can further contribute brother on the oil migration potential , within a 2T Premix engine . P.S. Oil Injected systems also inject directly to the small & big end bearings or directly into the intake runner to be aspirated into the fuel charge , although not within saws that iam currently aware ?

One hopes the oil doesn't vaporize in the crankcase. If it does its because the engine is running on the edge of failure. You can visualize this by inspecting the underside of the piston crown for "death ash".

 

[North by Northwest]

One hopes the oil doesn't vaporize in the crankcase. If it does its because the engine is running on the edge of failure. You can visualize this by inspecting the underside of the piston crown for "death ash".

No , i meant when it meets the intense heat of combustion , & falls out of solution , (wetting metal surfaces) it would wet the wrist pin & piston skirt & ring assembly . I would not wish the crankcase being that hot & flashing lol . What other migration potential do you recognize ? lol.

 

[Automender]

Seems by going by the color of the smoke, which in my case is blue and not black soot, the smoke is caused by unburned oil. If you soak a rag in gas and light it it produces black smoke. I know that the 2.6 oz of oil in a gallon of gas doesn't build up in the crankcase and migrates to the cylinder so it is carried by the mixture of air and fuel. If you think about it the oil particles are dragged by air and gas vapor. I suppose one can figure out the heavier density gas, that being either air or gasoline will carry more oil. By volume with a 15 to one ratio of air to gas mix the air moves more oil than gas. Basically it works like the refrigerant and oil movement in a AC unit.

 

[link]

40:1, because it is a round figure. And very safe indeed.

 

[ApePilot]

I did not hear back on your numbers brother , however recently woods ported a quad port 357 xp . I ran with a conservative .018 squish , 141 duration & 13.5 deg. of blowdown & achieved a 500+ rpm gain over stock with a minor muffler mod & goobs of low & midrange torgue . The overall compression with the crank stuffers wa. pretty well unaffected . I still run 91 octane with Saber @ 44:1 . Very strong firewood saw. P.S. I usually use a 10 deg. raduis on all chamfers including the transfers .

Sorry NNW, been busy trying to get my new (stupid) P320 XTen running right. Mags keep jamming-up with 200 gr HC. Sig sucks.
Anyway, the 3120xp:
Exhaust opening = 98 deg ATDC, duration = 164 deg.
Intake duration = 135.7 deg
And oops, looking at my spreadsheet on the engine, squish is actually 0.580mm = 0.0228" (still kinda tight for the compression and squish-band width of 9.5mm)
I've been thinking of getting it just a hair tighter.... but calcs indicate that it's already too tight. No indication of detonation with the fuel being used, though.
Blowdown is just a hair over 22 degrees.
Transfer duration is 120 deg.
Nothing too radical, though I don't know if I want to try 93 octane as before. Seems to run smoother and harder on 100LL for the time being. And Aviation fuel is no more expensive than the available non-alcohol 93 pump gas around here.
I've been thinking of increasing intake duration to around 140 - 142 deg.
The head, piston deck, and intake and exhaust ports have had the 350 deg baked Cerakote Piston-Coat applied and it does seem to help with keeping the heat inside the combustion chamber rather than getting the piston undersides and head too hot.
I use pretty cool plugs -- B10HS.

Funny (not), I have the engine apart again, checking things out. I purchased an OEM piston last year to put on the shelf for a snowy day. I just weighed it and it's a whole 2.3g lighter than my messaged and lightened OEM piston that I had been running. WT....? Measured it all over and found some of the webs are slightly thinner, but the big surprise was some minute cracks in the casting right at the window/skirt corners just under the lower ring, on two sides. Bugger. Good luck exchanging that piece of junk AL.

The OEM rings (junk) that I had in there lasted maybe 1.5 hrs. Initial gap was something like 0.445mm, should have been closer to 0.21mm. I ran them anyway because I couldn't find any G15H cabers at the time. Everyone was selling those F-Cast rings.

The thing ran really powerful for about half hour straight out of the shop (typical break-in stuff, short bursts up to roughly 11000rpms). Then the rpm's started slowing down roughly 200-300 rpm's lower (tinytach). No big deal though. After 1.5 hrs, took the pipe off and saw minute scratches on the cylinder on the intake side. Fug!
Took the top off and found minute scratching on the exhaust side too. Double fug! Ring gap grew to 0.650mm on both rings! Max-gap replacement time should be around 0.60mm. These husqvarna OEM rings suck. They're lazered 'KO B8' for Komarov s.r.o. The circumferential exterior edges of the rings looked a bit chipped in some places, but not really localized to the ports. Initially the edges were quite sharp, not chamfered.
Finally got some G15H cabers in yesterday. Nicely chamfered edges. Gaps acceptable at 0.253mm.
Crankcase has been thoroughly flushed, all bearings look and feel good, seals are 1.5hrs old, so going to slap on the rings and see how she goes. Again.
Anyone know where I can find a Meteor piston for the 3120, or should I just get another OEM at inflated cost?

 

[North by Northwest]

Sorry NNW, been busy trying to get my new (stupid) P320 XTen running right. Mags keep jamming-up with 200 gr HC. Sig sucks.
Anyway, the 3120xp:
Exhaust opening = 98 deg ATDC, duration = 164 deg.
Intake duration = 135.7 deg
And oops, looking at my spreadsheet on the engine, squish is actually 0.580mm = 0.0228" (still kinda tight for the compression and squish-band width of 9.5mm)
I've been thinking of getting it just a hair tighter.... but calcs indicate that it's already too tight. No indication of detonation with the fuel being used, though.
Blowdown is just a hair over 22 degrees.
Transfer duration is 120 deg.
Nothing too radical, though I don't know if I want to try 93 octane as before. Seems to run smoother and harder on 100LL for the time being. And Aviation fuel is no more expensive than the available non-alcohol 93 pump gas around here.
I've been thinking of increasing intake duration to around 140 - 142 deg.
The head, piston deck, and intake and exhaust ports have had the 350 deg baked Cerakote Piston-Coat applied and it does seem to help with keeping the heat inside the combustion chamber rather than getting the piston undersides and head too hot.
I use pretty cool plugs -- B10HS.

Funny (not), I have the engine apart again, checking things out. I purchased an OEM piston last year to put on the shelf for a snowy day. I just weighed it and it's a whole 2.3g lighter than my messaged and lightened OEM piston that I had been running. WT....? Measured it all over and found some of the webs are slightly thinner, but the big surprise was some minute cracks in the casting right at the window/skirt corners just under the lower ring, on two sides. Bugger. Good luck exchanging that piece of junk AL.

The OEM rings (junk) that I had in there lasted maybe 1.5 hrs. Initial gap was something like 0.445mm, should have been closer to 0.21mm. I ran them anyway because I couldn't find any G15H cabers at the time. Everyone was selling those F-Cast rings.

The thing ran really powerful for about half hour straight out of the shop (typical break-in stuff, short bursts up to roughly 11000rpms). Then the rpm's started slowing down roughly 200-300 rpm's lower (tinytach). No big deal though. After 1.5 hrs, took the pipe off and saw minute scratches on the cylinder on the intake side. Fug!
Took the top off and found minute scratching on the exhaust side too. Double fug! Ring gap grew to 0.650mm on both rings! Max-gap replacement time should be around 0.60mm. These husqvarna OEM rings suck. They're lazered 'KO B8' for Komarov s.r.o. The circumferential exterior edges of the rings looked a bit chipped in some places, but not really localized to the ports. Initially the edges were quite sharp, not chamfered.
Finally got some G15H cabers in yesterday. Nicely chamfered edges. Gaps acceptable at 0.253mm.
Crankcase has been thoroughly flushed, all bearings look and feel good, seals are 1.5hrs old, so going to slap on the rings and see how she goes. Again.
Anyone know where I can find a Meteor piston for the 3120, or should I just get another OEM at inflated cost?

Impressive amount of work brother , I checked my notes Exh ATDC 103 Deg. Duration 141 deg. Transfer ATDC 123 deg. Blow down 13.5 deg. Int. ABDC 106 Duration 143 deg. Even with the conservative squish it is very responsive in the cut . I went with a Meteor Piston with Caber rings from Saws again . Com . As previously mentioned I run 91 octane Sunoco Premium , I trialed Ultra 93 but did not perceive any performance or runibility gains . I fabricated the muffler mod of the stock muffler also , with a deflector to a 3/8" exhaust stub aka " Ironhorse clone " . If anything , I perhaps should have popped another $10 for a Dukes Moly coated piston . Next time perhaps lol .

 

[ApePilot]

Impressive amount of work brother , I checked my notes Exh ATDC 103 Deg. Duration 141 deg. Transfer ATDC 123 deg. Blow down 13.5 deg. Int. ABDC 106 Duration 143 deg. Even with the conservative squish it is very responsive in the cut . I went with a Meteor Piston with Caber rings from Saws again . Com . As previously mentioned I run 91 octane Sunoco Premium , I trialed Ultra 93 but did not perceive any performance or runibility gains . I fabricated the muffler mod of the stock muffler also , with a deflector to a 3/8" exhaust stub aka " Ironhorse clone " . If anything , I perhaps should have popped another $10 for a Dukes Moly coated piston . Next time perhaps lol .

Interesting that you mentioned 'stuffers.' I've been concentrating on other parts of the engine, but have reserved increasing the primary compression figures (crankcase compression) for miserable rainy winter days.
How did you fabricate the stuffers and how did you secure them in place? Did you add any additional weight (tungsten?) to the lobes to help balance the extra weight of the stuffers? Also, did you notice any more torque at higher RPMs due to the higher compression ratios? What kind of ratis did you start with, and what did you end up with? I'm guessing that any small gains would be hard to feel in sawing firewood, but in a saw-mill rig it might be more apparent.
What was your intake duration before your porting? What kind of improvement did you see with the 143 deg duration? More higher-rpm torque?
Thanks NNW!
-doug