Is running 40:1 in a 50:1 saw a big deal?

D

Donuts

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Apr 24, 2025
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I'm about to grab a new saw that needs 50:1 fuel, but I've got 3/4 gallon of 40:1 premix, is it a big issue if I run the 40:1 in the new saw, or should I just toss it?
 
You should be just fine to run 40:1 in a saw that specifies 50:1. I run 45:1 in all of my two strokes that call for 50:1. I find doind that helps with engine performance and also keeps the parts from wearing as fast.
The only thing I will tell you is your muffler screen will clog much quicker on a 40:1 mixture. That will be especially true if you are continuously running the saw at low RPMs.
 
Stihl_Fanatic said:
You should be just fine to run 40:1 in a saw that specifies 50:1. I run 45:1 in all of my two strokes that call for 50:1. I find doind that helps with engine performance and also keeps the parts from wearing as fast.
The only thing I will tell you is your muffler screen will clog much quicker on a 40:1 mixture. That will be especially true if you are continuously running the saw at low RPMs.
Click to expand...
I figured a little extra oil wouldn't hurt, but good point about the muffler screen., I'll keep an eye on it and avoid low RPMs too often.
 
I run 40:1 in all my saws and that came from a chainsaw tech years ago. He wasn"t a fan
on running 50:1 in them. As he said a wee bit more smokier but a bit more oil in them
too which he said is better for them.
 
Leon Couper said:
I run 40:1 in all my saws and that came from a chainsaw tech years ago. He wasn"t a fan
on running 50:1 in them. As he said a wee bit more smokier but a bit more oil in them
too which he said is better for them.
Click to expand...
That's the way it was told to me too. Except I always use 42-45:1. I do of one guy, though, who runs something like 30:1 in all of his two stroke no matter what the manufacturer says you are supposed to use.
 
I bought a "Supmix" saw to leave at our place in Maine. The manual saws it needs 25:1 mix. I've run 7-8 tanks through it & figure once it's had 10 tanks it'll be broken in. At that time, I'm going to switch to 50:1 for simplicity. The 25:1 is so smokey on still days, it is annoying.
 
Leon Couper said:
I run 40:1 in all my saws and that came from a chainsaw tech years ago. He wasn"t a fan
on running 50:1 in them. As he said a wee bit more smokier but a bit more oil in them
too which he said is better for them.
Click to expand...
I'll stick with 40:1 for now since it seems to work well
 
Rich said:
I bought a "Supmix" saw to leave at our place in Maine. The manual saws it needs 25:1 mix. I've run 7-8 tanks through it & figure once it's had 10 tanks it'll be broken in. At that time, I'm going to switch to 50:1 for simplicity. The 25:1 is so smokey on still days, it is annoying.
Click to expand...
I get that the 25:1 mix can be a bit much, switching to 50:1 after the break-in makes sense for less smoke and easier maintenance.
 
Oil Mix ratio .
This is my opinion, backed by some science.
Assuming you use a good quality oil. Made for AIR cooled 2 strokes.
35 to 40 to 1 is going to give the best compromise between general lubrication requirements. Piston ring sealing, and power.
Less oil= more petrol air mix in cylinder =more power but also = less lubrication, more friction, more heat, less sealing by the piston rings.
More oil = the opposite
Tests in racing 2 stroke motorcycles generally end up with a figure of 35 to 40 to 1 as working best.
Saws can be safe out towards 75 to 1 or even 100 to 1. But if anything else ain't quite right with anything....you will seize the saw. Even without siezeure wear will be accelerated. Noticeably.
25 to 1 will be smoky, and you risk plug fouling ,carbon build up and gummed piston rings.
Hope that helps.
Opinion differs . That is mine.
I've worked with 2 strokes and saws for about 50 years, though I didn't know much for the first few of them !


Donuts said:
I'm about to grab a new saw that needs 50:1 fuel, but I've got 3/4 gallon of 40:1 premix, is it a big issue if I run the 40:1 in the new saw, or should I just toss it?
Click to expand...
 
ChainSore said:
Oil Mix ratio .
This is my opinion, backed by some science.
Assuming you use a good quality oil. Made for AIR cooled 2 strokes.
35 to 40 to 1 is going to give the best compromise between general lubrication requirements. Piston ring sealing, and power.
Less oil= more petrol air mix in cylinder =more power but also = less lubrication, more friction, more heat, less sealing by the piston rings.
More oil = the opposite
Tests in racing 2 stroke motorcycles generally end up with a figure of 35 to 40 to 1 as working best.
Saws can be safe out towards 75 to 1 or even 100 to 1. But if anything else ain't quite right with anything....you will seize the saw. Even without siezeure wear will be accelerated. Noticeably.
25 to 1 will be smoky, and you risk plug fouling ,carbon build up and gummed piston rings.
Hope that helps.
Opinion differs . That is mine.
I've worked with 2 strokes and saws for about 50 years, though I didn't know much for the first few of them !
Click to expand...
Nope
 
I started running 45:1 to use up a gallon of Quick Silver outboard oil. So far so good, after running a few gallons of mix through various saws.
Subsequently, the random, different 2 cycle oils laying around have gone into this jug, maybe a pint altogether. The Echo dealer in town only sells their Power Blend Gold which is what I usually run at 40:1. Having never paid much attention to 2-stroke oils & never had a motor blow up makes me wonder about the myriad oil debates.
 
Rich said:
I started running 45:1 to use up a gallon of Quick Silver outboard oil. So far so good, after running a few gallons of mix through various saws.
Subsequently, the random, different 2 cycle oils laying around have gone into this jug, maybe a pint altogether. The Echo dealer in town only sells their Power Blend Gold which is what I usually run at 40:1. Having never paid much attention to 2-stroke oils & never had a motor blow up makes me wonder about the myriad oil debates.
Click to expand...
You might be flirting with trouble if you are running outboard oils that are designed for water cooled engines in and air cooled engine which is designed to run much hotter. The flashpoint of those two oils are vastly different.
 
I think over the years oil technology has justed ahead from the days of running sae30 for
2 stroke oil to what we buy today. That also is the same for chain oil from usung waste car oil
to what we get today real tacky and sticks to everything so get longer out of bars. when I worked in
sawmills in the sixties most of the Homelite,Canadians,IEL Pioneers and Solo,s all were half a pint to the gallon.
But that was normal oil. Even with todays oil if you are using normal 2 stroke oil stihl and husky I think off the top
of my head say 25to1 but if you use there oil the say you can go out to 50to1 so what are they doing different to
other companies. As I said in my first thread I use 40to1 in all eccept a couple of my real old girls and drop back to 32to l.
Never had any fouled up plugs either.
 
I run approximately 35:1 in my saws. They are tuned for the mixture. No smoke, never had to replace a plug, even in 8+ year old semi-commercially used saws. Nothing magical happens at any one oil mixture. I'm not anti 50:1 with today's modern formulas but a richer mixture isn't going to give you negative symptoms if the saw is tuned for the mixture.
 
Paul Aiken said:
I have gotten so I don't use my saws much. I have gone to the horribly expensive (canned gas') It is cleaner, easier to use, and lasts longer
Click to expand...
I store my saws, trimmers, blowers, etc in the late fall / winter with the motomix
I empty the tanks with my mix, start them run it out of the carbs, fill the tank just over the pick-up filter with motomix, start everything and let it run for about a minute, then store them.
 
It's counterintuitive but 40:1 will run slightly hotter than 50:1. Not enough to create issues in the short term, but just be alert to the potential pitfalls.

More oil in the gas means less gas in the mix, and the gasoline is where much of your engine cooling comes from.

Also more oil can increase compression, and therefore power output, by creating a slightly more robust seal between the rings and cylinder.

You can run down to probably 25:1 without major issues, as long as you tune the carburetor to compensate.
 
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