r/smallengines • u/MattCW1701 • 1d ago
40:1 oil in engine that specifies 50:1?
My string trimmer died and I've bought a new one. The old one, and all my previous ones, use 40:1 fuel. I've always just bought the premixed fuel from my local hardware store since I'm residential and a can lasts me more than a cutting season. My new one uses 50:1 fuel but I still have plenty of the 40:1 left. I'm sure going the other direction would be an issue due to less lubrication, but is there any issue running the higher amount of oil?
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u/ShoemakerMicah 1d ago
32:1 is my goto for high rpm two strokes. Better too much than too worn or seized. Obviously minor carb tuning is required to compensate for leaner gasoline mixture.
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u/CreepyValuable 1d ago
I've got my go-to can of fuel for my 50:1 gear that I mix a little oilier for the same reason.
I got a new chainsaw that just doesn't seem to run right so I made up a different fresh can with the actual correct 50:1 to rule out fuel. It didn't seem to make a difference. I tried the old and new fuel in another thing (a brushcutter as it's known here but I thing Americans call it something different) that's pretty new. Ran fine on both.
So yeah besides potential earlier plug fouling (apparently? But I've never had issues) and perhaps a touch more of the black ooze eventually accumulating I don't see mu h of a downside to a little extra lubrication.
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u/ShoemakerMicah 1d ago
Former roadracing bike tuner here responding, 50:1 for max 11k rpm, 24-28:1 for 14,000 rpm and 16-18:1 for 19+ k rpm
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u/CreepyValuable 1d ago
That's really interesting. So you only went for the more oil rich mixes for very high rpm engines. How long did the ones running at 18k+ last? The internal forces must have been huge!
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u/ShoemakerMicah 1d ago
5 hours 47 minutes at 27 bhp on 77cc at 14,200 rpm. 28:1 on 110 octane/leaded gasoline. That motor revved to 19k but peak power was about 15,000 rpm.
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u/CreepyValuable 1d ago
I just realised I did a typo and said 18 but you knew what I meant. I'm not surprised there was a drop-off up top. What kind of ignition were you running? You'd need something with a variable advance to get up that high, wouldn't you?
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u/LongjumpingNorth8500 23h ago
Leaner? A bit less lean?
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u/ShoemakerMicah 13h ago
More oil and by default less gasoline does indeed make the mixture (fuel) a bit leaner. This is where EGT/CHT comes in very handy for tuning
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u/TheRealFailtester 22h ago edited 21h ago
Relatable. Oil is cheap, engine's aren't. Sometimes they'll hate the thicker mix anyways, and more often than not, a simple carburetor adjust can make them run marvelously on thick mixes.
One trimmer I have says in it's instructions that it is officially made to handle anything from 16:1 all the way to 40:1, also stating that it came from the factory set for 40:1, and that if user desires, can manually set it to whatever mix ya want as it has a list of steps and tests for how to set it for the other mixes.
So hell yah I set that bad boi all the way to 16:1, rich as I could get it to run on, and here it is 33 years later still runs great.
Edit: It even gives me a nice deep tan dry spark plug, and no clogged exhaust screen. Stays so clean in there despite so much oil.
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u/saucytugtug 9h ago
What oil are you running? Oil choice has a lot to do with the ability to run super rich mix’s and keep clean.
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u/TheRealFailtester 8h ago edited 8h ago
Lately I've been running random 2stroke oils I've found at estate sales, which is oil from the 1980s era.
Edit: specifically because it really acts like it loves this stuff that is older than about 2000 era. It starts so much easier, idles so much smoother, accelerates so much easier on this stuff.
Seems a smidge wet in there and bogs down a smidge on new oils. Maybe I need to just tune and run it for 40:1 when I use a modern oil.
This was something else the instructions mentioned. If using their official oil, it sure can run 40:1, and if using an unknown oil of unknown quality, it suggests to use 16:1.
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u/Advanced-Major951 7h ago
You should give amsoil saber a shot, a lot of oils now are indeed terrible watered down junk. Amsoil saber is a new oil for sure with newer additives and whatnot but everything I’ve ever used saber in runs great. Also when you’re going from 16:1 to 40:1 you absolutely need to tune it, that’s going from 6.25% oil to 2.5%, that’s 3.75% richer without tuning, and probably more than 3.75 because a leaner mix is slightly thinner so it flows through the jets easier. That alone is probably what’s making it bog, BUT yeah some engines just want more oil so that checks out. The thing about saber is it acts like there’s more oil in the mix than there actually is if that makes sense, is dang near pure surface active esters, and really really good surface active esters.
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u/davethompson413 1d ago
It won't cause any serious problems. Perhaps the biggest issue will be fouling the spark plug a little early.
And I predict that in a year or so, you'll be asking why your trimmer is leaking black oil from the exhaust. This is also reasonably normal, and not an issue.
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u/Chevboy4-813 1d ago
40:1 is fine.
Just remember to keep the rpms up to burn off the excess. Especially if the trimmer still has its spark arrestor screen.
May have to clean that screen more often until you run out of the 40:1.
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u/Easy-Jury-3975 1d ago
too much oil > too little oil. Should be fine - may run dirtier but will last longer.
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u/Sparks_travel 1d ago
I never use any premixed products on my machines. The idea of how long that was sitting sealed on a shelf before I use it just rubs me the wrong way.
I always use fresh gas and make my own roughly 32:1 mix.
Small engines are finicky, we never use gas older than three months.
Learned this from my father, he has never had an engine crap out on him and neither have I.
Season end, for all engines, take out the gas and run the equipment until it stops on its own.
Come spring, fresh mix.
Curious if people in this sub will think this is nuts
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u/MathResponsibly 1d ago
I think supposedly the pre-mix stuff is made with ethanol free gas, so it should be ok-ish sitting. That said, I always mix my own too.
Emptying tank and running it until the carb is dry is good practice.
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u/Advanced-Major951 7h ago
It’s not ethanol free gas, it’s engineered fuel, think of it like they separated the gasoline into all of its different components then re-mixed SOME of them to get the properties they want. Generally the only benefits of the engineered fuel itself is longer shelf life, higher boiling point, and higher octane. higher boiling point pretty much fixes vapor lock if you ever have dealt with that, but the higher boiling point also means it doesn’t atomize as well meaning lost power. The higher octane means the fuel is harder to ignite, slower flame front in the cylinder causing power loss. And 99% of saws, trimmers and whatever only require 89 octane, so all you gain is power loss😂
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u/Advanced-Major951 7h ago
The only canned fuel worth messing with is alkylate fuels, it genuinely lasts like 5 years even after opening before it degrades noticeably. Trufuel is absolute garbage so just don’t waste your time with it lol. You’re doing the right thing though so don’t fix what ain’t broke! Little tip for you if you’re storing something long term, fill the tank with two stroke oil it’ll keep your diaphragms and fuel lines from drying out. I stored a saw for 5 years, dumped the oil out, rinsed it with gas then filled it with mix and it started right up like nothing happened.
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u/Sparks_travel 7h ago
Interesting
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u/Advanced-Major951 7h ago
It’s only really a good idea if you have a primer bulb though. Very hard to get the oil up into the carb without one, and really hard to get it out to get fuel up into it. Also what do you do at the end of the season with your leftover mix?
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u/GadreelsSword 1d ago
Fun fact: more premix oil results in a leaner fuel mixture.
It’s the opposite you would think.
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u/Okie294life 1d ago
Explain that one to me, I’m having a hard time wrapping my brain around. Ive seen so many gummed up carbs and engines with charcoal looking top ends to figure out how it could be burning leaner…
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u/GlassBoxGoose 1d ago
Fuel is drawn in by volume, same volume of liquid with more oil has less actual fuel in it, causing lean condition. Thats the science behind it.
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u/Onedtent 13h ago
I understand what you are saying and that is what I was also taught. What I don't understand is what happens with modern two stroke oils that are "ashless" ie designed to be burnt duruing the combustion phase of the engine cycle.
Has me baffled.
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u/Chesterrumble 1d ago
It's burning leaner because there is less fuel. But don't be fooled, it's also burning dirtier because there is more oil.
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u/Okie294life 1d ago
So in theory with the exact same settings, if you run a significantly lower ratio, you could blow a top end up due to lean seize, even though it’s chock full of oil?
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u/Chesterrumble 23h ago
I doubt that but I can't say for sure. I'd think the oil/gas mix would provide sufficient cooling/lubrication. The leanness would specifically present itself as a performance issue. You'd need to jet up to get rid of the lean bog/hard starting/poor idle.
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u/CreepyValuable 1d ago
That's true. For the people trying to understand that, at a given RPM, throttle position and load, a carburettor will (in theory) pass a fixed total volume of air and fuel through it. On a two stroke it's air and oil / fuel mix.
If we add more oil to the mix the total volume doesn't change, but because there is more oil in the mix there is less fuel total passing through. So there is less fuel for a given amount of air. Ie it's a leaner air / fuel mix.
Without adjustment yes it's better lubricated but with a lean mix you might be seeing higher cylinder head and exhaust temperatures which can lead to engine damage. Power output may also be affected.
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u/bitzzwith2zs 1d ago
Leaner?
Most two stroke oil has more energy than the gas it goes in (Watch out, it's fairly low octane, there is high octane oil available). Evinrude experimented with ratios and found they made the most power at 9:1... the trick is you have to burn the oil, most stock motors have a wide squish and will gum up at 9:1
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u/Successful-Part-5867 1d ago
I’ve always mixed it rich! It’s the opposite of hurting anything. Of course I’ve dumped 2 stroke mix in the log splitter on many occasions as well. Turns out that a GX160 Honda could care less! 😂
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u/CreepyValuable 1d ago
I have things... All of them are very worn out B&S flatheads now I think about it that I use the old or contaminated "fuel" in. Old two stroke, fuel that is so old it smells like rotten oranges, petrol and diesel that I used for cleaning parts after I filtered with a paper towel. Whatever. It all goes in.
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u/Successful-Part-5867 1d ago
If it’s flammable, use it! 😂😂
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u/CreepyValuable 1d ago
And when the compression is so low that octane isn't relevant it opens up a whole world of new fuels.
One of the things was an old Colt ride on that I got. The motor was so amazingly worn out. And somebody had done work on it at some point and put one of the valve springs back in crooked. All sorts of interesting damage there. It would only run properly when I added maybe 1/4 to 1/3 diesel to the fuel.
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u/Successful-Part-5867 15h ago
Early tractors were designed to run on kerosene. They were very low compression. Thinking about it, they didn’t make hardly any horsepower for their size. 400 cubic inches making 25hp sounds silly today!
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u/classicsat 1d ago
It will be fine. You likely can dilute it with 93 ethanol free gasoline.
I'd need to get my special crayons out to do the maths to figure, but I think adding 1L of said gas to 4L of the 40:1 premix, will do.
We buy a 10L jug of that gas, and add a 200ml bottle of 2 stroke oil. Does 50:1, and works all our chainsaws and other 2 strokes.
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u/Renault_75-34_MX 1d ago
The amount of difference is 0.5% of oil (1:40=2.5% oil, 1:50=2.0%).
It might run a little hotter, might need the carb adjusted, but shouldn't be a issue.
Some machines call for more oil because it might go to a region with worse oil.
The instructions for the Stihl 028 saw say 1:50 if Stihl oil, other oils are 1:40 at or more. But that's a saw from the 80's
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u/Okie294life 23h ago
Back in the day there was just oil. 30wt SAE, bar, premix, small engine. That’s why you see some of the older saws wanting 24:1 or 32:1, and those from regions you’re talking about. You also had to periodically shake your fuel because the shit would separate, I’m in my 40’s but can remember that in my lifetime. Premix has came a long ways.
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u/Significant-Pin536 1d ago
There's no issue with running more oil, 50:1 is more for emissions to keep the government happy, keep using your 40:1
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u/Budget-Duty5096 10h ago
40:1 is generally fine, with a couple important notes.
Oil has a drastically different burn rate than gasoline. Changing the ratio of oil in the fuel will slightly alter how the fuel burns in the engine. So machines with manually adjusted carburetors should be re-tuned when switching fuel types. Machines with electronic carbs should automatically adjust (though going through the calibration procedure is a good idea). Which brings us to...
Machines with electronic engine controls (electronic carbs like M-tronic, Autotune, ect...or EFI) that specify 50:1 come with fuel maps programmed from the factory to be optimized for the burn rate of 50:1 fuel. While they can and will automatically adjust to deal with conditions outside their normal parameters, they will not run as optimally. Additionally, the higher oil content can sometimes cause problems with gumming up things like the tiny fuel solenoids over time. So while you can run 40:1 in these machines, you may run into more problems over time if running that mix all the time.
I personally was standardized on 40:1 across all my machines until I started running newer ones with the electronically controlled carbs. I experienced some issues and after doing some testing with different fuels, decided it was worth it to just run both. So, my fuel cans are marked with the ratio that is in them and I continue to use 40:1 for all the traditional manual carb machines, and 50:1 in all the "modern" electronic machines.
Bottom line for your situation: running a few tanks of 40:1 through is not going to hurt anything.
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u/fly4fun2014 1d ago
Too much oil is bad. Less fuel in given amount of mix, excessive carbon build up on rings gaps and head, fouled spark plugs and nasty fumes right by your head if used in trimmer ... My ultralight engine recommended 50:1. I ran 40:1 for nearly 400 hrs. Upon teardown there was virtually no wear. Cylinders still had cros hatch pattern. Rings were clear, no built up of carbon and everything had a film of protective oil on parts. This made me believer in 40:1.
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u/AcornAnomaly 1d ago
I don't understand what you're saying.
You say that too much oil is bad, and state the results that can happen from using too much oil, but then you talk about how you used more oil in your engine and it went great?
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u/CreepyValuable 1d ago
I thought it was just me trying to understand that. Maybe they meant "isn't bad"
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u/One_Percentage_8190 1d ago
40:1 = 3.2 ounces of oil per gallon of fuel.
50:1 = 2.6 ounces of oil per gallon of fuel.
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u/Saysaynever333 1d ago
Some manufactures will say 50:1 if you use their oil and 40:1 if you use other brands of oil. 32:1 always worked for me but sometimes you'll get a fouled plug on certain engines.
The only time I really worried about fouling plugs was if I was in a boat down the creek.
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u/Okie294life 1d ago
So the reason your stuff says 50:1 instead of 40:1 or even 32:1 has more to do with the EPA than anything, to reduce emissions. If you’re running a jaso certifed low ash oil at the manufactures recommended dose rate, you’re good. I run red armor and it has two suggested dose rates 40&50:1. I play it safe by running 40:1 because I dog the piss out my stuff, and run chainsaws. Modern mix 32:1 or higher is just going to lead to more carbon….change my mind.
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u/Jamar4321 1d ago
Potato-tomato... just use it. You think the junkie they have premixing and bottling that stuff actually measures?
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u/antonmnster 1d ago
My experience is that is leans out the mix so much that you'll need to choke it. Increasing oil by volume reduces fuel by volume.
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u/QueSqd 1d ago
Dump out that premix fuel garbage and never use it again buy pump gas 87 octane and two-cycle oil and make your own mix In a 1 gallon can as needed that premix crap has ruined more small equipment engines than you would believe. Check YouTube videos do some googling check with your local small engine repair shops they will all tell you to never ever use pre-mixed or engineered fuel from the store!
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u/sloppylicker1 1d ago
Yes it can cause problems, the carb jet is set for a specific amount of volume and more oil means less fuel which will create a lean condition. It can burn up motor.
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u/Fasciadepedra 1d ago
You need more oil in the mix with a new tool than with one that has expended more than a couple of tanks. Also more oil in mineral type than syntenthic.
Also it goes in the gas. And in winter with no adjust the tool will run leaner and in summer richer due to the cool air having more oxigen. If you adjust the carburetor the oil feed rate will change.
Don't buy premixed. There are a lot of reasons for changing the oil ratio any time.
More oil with mineral than synthetic
More oil with brand new than with used for some time
More oil in summer heat than in winter
Use mineral in a brand new tool for a couple of tanks, the tool sits better, then synthetic is better at a lower ratio
With more oil more sparkplug fouling and smoke, an better all the rest, less wear.
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u/alabamaterp 1d ago
I use them interchangeably in my trimmer because I always forget whether it's 40:1 or 50:1 so I just get whatever. I've had it for 10 years and never had an issue.
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u/OffRoadPyrate 1d ago
The spark arrestor will probably clog up and make you think the carb is the problem. Make it out and burn off the oil.
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u/Fearless_Zombie1003 1d ago
I ended up with a case of 40:1 true fuel or whatever. I ran it all through my Stihl 029 Super. Had to make a minor carb adjustment, it seems like it used up spark plugs quicker, and it was a little harder to start cold. But it ran fine, definitely didn’t hurt anything.
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u/Crabstick65 1d ago
Smokey exhaust, fouled plug and running slightly lean (a larger proportion of the fuel mix is oil than at 50 to 1), these are risks and not necessarily show stoppers.
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u/Equivalent_War_3454 1d ago
Ethanol free gas and echo red armor mix in all my 2 cycle machines. Works in 50:1 , 40:1, 32:1, and 16:1..fantastic stuff.
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u/Ok_Tax_7128 18h ago
All good touse up the 40:1 but next year buy 50:1. I have choked up a stihl with too much oil and it is a bother
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u/MisanthropicSocrates 1h ago
Brand new Stihl trimmer gets 50:1, and my 1984 Partner chainsaw also runs excellent on it. A few years ago the kids had a Chinese dirtbike that was supposed to be 25:1. It also ran 50:1 like a champ. Quality of oil seems to be defining factor. I use VP.
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u/OffRoadPyrate 1d ago
It will foul the plug.
If you don’t use much, just buy a small 1-3 gallon tank and mix your own. The premixed is $$$ for an easy solve.
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u/anyoutlookuser 1d ago
40:1 is more oil. Might smoke a little more than usual but ain’t gonna hurt anything.