40:1 or 50:1 gas mix

Does it really matter if you use 40:1 or 50:1? I?m working on a weedeater for a friend it says 40:1. All I have around here is 50:1. I?ll probably mix up some 40:1 just curious on opinions.

50:1 will work just fine. However, many 50:1 engines don't like being fed 40:1 mixtures. Not enough lubrication.

(quoted from post at 07:34:18 06/14/18) 50:1 will work just fine. However, many 50:1 engines don't like being fed 40:1 mixtures. Not enough lubrication.

Click to expand...

You have it backwards sir. 40:1 has more lubricating oil per volume and per weight than 50:1.

40oz fuel to 1 oz oil = 2.5% oil to fuel mixture

50oz fuel to 1 oz oil = 2% oil to fuel mixture

I do 25 to 1 in all my 2 cycle engines. And don't notice any extra smoke either. My old friend that was a small engine repairman recommended 16 to one in everything 2 cycle.
He said engine would last much longer. Never had a problem using 25 to 1 as long as you are working the engines and not just letting sit and idle.
Richard in NW SC

(quoted from post at 07:10:19 06/14/18) Does it really matter if you use 40:1 or 50:1? I?m working on a weedeater for a friend it says 40:1. All I have around here is 50:1. I?ll probably mix up some 40:1 just curious on opinions.

Click to expand...

Use the 40:1 in that weedeater. Although oils have improved, and machines have become more tolerant of less oil mix, it may be an older machine that was designed for 40:1. If you use 50:1 it will work well at idle and low power but may overheat at high output.

Most of the remaining 2 stroke engines out there(except small weedeaters, blowers) use oil injection with a variable ramp mixture set by throttle. Yamaha 2 stroke jet skis set about 60:1 at idle, and gradually increase the ratio to 35:1 at full throttle where upper cylinder lubrication demands are greater. (they aren't made anymore, all 4 stroke now)

Back in the 50s, mix ratios were much higher. 2 stroke drone engines from McCulloch were 20:1. Of course the oil wasn't very good back then so they needed a lot.

(quoted from post at 07:38:36 06/14/18)

(quoted from post at 07:34:18 06/14/18) 50:1 will work just fine. However, many 50:1 engines don't like being fed 40:1 mixtures. Not enough lubrication.

Click to expand...

You have it backwards sir. 40:1 has more lubricating oil per volume and per weight than 50:1.

40oz fuel to 1 oz oil = 2.5% oil to fuel mixture

50oz fuel to 1 oz oil = 2% oil to fuel mixture

Click to expand...

Dang, you're right. ...Sure wish I could figure out which end of my brain to figure from! *lol*

Thanks Doc.

I only mix 43-1, that's 3 oz per gallon. My 11 engines are anywhere from new to 46 years old, they all run great and last a long time.

You want opinions, so here's mine...

I would run 50:1 premium synthetic oil. Be sure it is for air cooled engines.

I run it in everything, never had a problem. Chances are you are not running the weed wacker at full throttle and full load continuously. The max oil ratio is only needed under those conditions. Even then, if a chain saw can handle 50:1, and run full power, everything else should be a breeze!

What I have seen from running too much oil, and running cheap generic oil, it tends to carbon up the exhaust side of the piston and cylinder wall. The carbon gets in the ring land, sticks the ring, also the build up and crowds the piston over, loosing clearance to the point of having a seizure.

my old Johnson outboards took 16 to 1 ratio

I have since about 1999 have use Opti-2 in every thing and one mix works in every thing. I have used it in saws and weed eaters that were over 25 years old to new machines. I have run it in McCoulloch,Husky, Homelite,Poulan, Stihl, and Echo and saws run clean no smoke and longer plug life and one mix of fuel to run them on.

the reason for the ratios is the engine manufacturers have set up what they think is the minimum oil ratio based on the cheapest, junkiest oil on the market. apparently some engines need more than others.

IF IF it is GOOD 2-stroke oil you can use the lighter 50:1 in the 40:1 engine.

AMSOIL stands behind their Saber 2-stoke oil at 100:1 in any 2-stroke engine. I've used it (dealer) in a couple of my weed-wackers with no issues.

Correct! 40 or 50 to one is as you say. I have some really old Mall
and Disston saws. Also Mc Culloch saws that go back to their second
model. I run everything 36/38 to one. Have several Eagle saftey cans
that I have found over the years that were purposely made with a 3/4
gallon capacity. Throw in a bottle of GOOD quality oil "major
manufacturer name" and 3/4 gallon of Hi-test gas. Everything I have
just runs clean and dandy. Those real old saws when mixed 16 to one
and were running with 40wt motor oil. Smoked like a steam locomotive.
The synthetic oils are fabulous in comparison. What needs to be
remembered.....50 to one is to meet the polution BS standards. They do
NOT care if you blow your engine after a short life. I'll take my
36/38 to one mix anyday.

Lots of good comments from long-time 2 stroke users here. The switch to higher ratios had a lot of things at work. Much better 2 stoke oils, change to mostly synthetic(although the base stock is really not a true syn, it is a dino base), better metalurgy for 2 stroke pistons, cyl and rings, and of course - EPA regs.

Older 2 strokes used more fuel as well, with stoichiometric ratios running as rich as 11:1, where a perfect fuel air mix is about 13.2:1. As the engine runs leaner, it also gets less lubrication. The modern oils and modern metals can handle much lower oil mixtures at leaner settings, and the older engines seem to survive ok mostly due to the higher stoich of air/fuel. The carbonizing deposits are a mix of oil, and unburned fuel. However, don't try to run an older engine leaner, or if one does, then one must increase the oil mixture to insure adequate lube of the upper cyl. A 20-30 YO saw, or other 2 stroke will NOT run well with a lean mixture of 13:1 with a 50:1 oil mix. It will overheat, it will seize(eventually).

Injection-lube in jet skis, and snowmobiles came about because engines were blowing up with a pre-mix of 50:1 as those engines are beat to death by kids who go out and run full throttle constantly. The EPA got into it as well with new regs on emissions and the mfg tried to meet the new regs. Water cooled engines have a different requirement than air cooled, but they can work pretty close.

I would(and do) feel comfy running almost anything around 40:1 pre-mix. I don't like 50:1 unless I know the engine is not going to be worked real hard, or I know I can change the stoich mixture with a screw at the carb. Most small 2 strokes no longer allow the mixture screw to be moved, but some have it, and it's covered by a plastic snap cap. The other countries allow the mixture to be set, but in the US that feature is disabled(unless one removes the plastic snap cap).

If you have a mixture screw, note that it may be for the high RPM, or it may be for low RPM. Adjust with caution and read the plug after running for less than an hour. A white, or super clean plug indicates too lean, and that will lead to damage. It should be nice and tan, or a light chocolate for best stoich.

I run some 2 stroke aviation engines, and we are super-critical on oil, mixture, stoich, and general condition of the plugs each 5-10 hours of run time. Mistakes in aviation engine running can be very costly, or painful.

I mix with Stihl oil 2.5 gallons at a time. It comes in the pre-measured bottles and mixes at 50:1. I use it in anything 2 stroke. Never any issues.

Me too.

Hello old650,

No problem, put you mix in and run it! Just do not adjust the carb, or adjust it after he puts in his mix. It may not make a difference. But hose jets are soooooo small........... it might,

Guido.

Hello Richard G,

Your owners manual should be Your bible. Absolutely no reason to deviate from it.
Lean conditions are the #1 reason for smoking pistons,

Guido.

My experience, the 50/1 machines wont like 40/1(detonate, run lean,foul plugs), while the 40/1 machines seem to run great on 50/1. I have been doing that for years on old Lawnboy 2 cycle push mowers made for 40/1. Discussion on a lawn / garden site is that only the very old sleeve bearing 2 cycle engines will not last on 50/1 with modern oil. Anything with a roller / ball bearing crank does just fine.

Me 3, but my little synthetic jugs say for 2 gal, or 1 gal. No 2.5 gal.
Loren

Had me second guessing myself for a second....

It would be nice if the 2 cycle engineers would get together and pick one fuel ratio wouldn't it. I have a lawn mower which is 32:1, a weed eater that is 40:1, and a chain saw that is 50:1. I have to keep five cans of fuel around here if you include a gas and a diesel tractor.

(quoted from post at 10:10:19 06/14/18) Does it really matter if you use 40:1 or 50:1? I?m working on a weedeater for a friend it says 40:1. All I have around here is 50:1. I?ll probably mix up some 40:1 just curious on opinions.

Click to expand...

If some is good then more is better..............not always.
Adding lube oil to the gasoline lowers the fuel's octane rating. Detonation or knock can ruin and engine just as fast as no lube oil will.

Since 50:1 is pretty much the norm these days for 2 strokers, when a chainsaw or weedeater mfgr. specifies 40:1 I figure they spec it for a reason. I had a couple of whackers loose rings at what I thought was prematurely. I was using full syn at 50:1, Stihl silver. After the OH, decided to up it to 40. We'll see how it goes.

(quoted from post at 08:15:47 06/14/18)

(quoted from post at 07:38:36 06/14/18)

(quoted from post at 07:34:18 06/14/18) 50:1 will work just fine. However, many 50:1 engines don't like being fed 40:1 mixtures. Not enough lubrication.

Click to expand...

You have it backwards sir. 40:1 has more lubricating oil per volume and per weight than 50:1.

40oz fuel to 1 oz oil = 2.5% oil to fuel mixture

50oz fuel to 1 oz oil = 2% oil to fuel mixture

Click to expand...

Dang, you're right. ...Sure wish I could figure out which end of my brain to figure from! *lol*

Thanks Doc.

Click to expand...

kcm, I think you're thinking not enough FUEL.

A 40:1 mixture can be too LEAN for some 2-stroke engines that are expecting 50:1. That's worse than not enough lube, a recipe for a scored cylinder and galled piston.

I use a synthetic Amsoil in a 1 gallon jug and make 5 gallons at a time. I use non-ethanol recreational fuel and add some Seafoam to each batch. I mix at 40:1 and run in everything from 16:1 to 50:1 with no issues. The rec fuel has eliminated my carb issues. I have at least 15 2 stroke tools.

arent you backwards 40-1 would be less gas than 50-1

(quoted from post at 11:45:07 06/14/18)

(quoted from post at 07:10:19 06/14/18) Does it really matter if you use 40:1 or 50:1? I?m working on a weedeater for a friend it says 40:1. All I have around here is 50:1. I?ll probably mix up some 40:1 just curious on opinions.

Click to expand...

Use the 40:1 in that weedeater. Although oils have improved, and machines have become more tolerant of less oil mix, it may be an older machine that was designed for 40:1. If you use 50:1 it will work well at idle and low power but may overheat at high output.

Most of the remaining 2 stroke engines out there(except small weedeaters, blowers) use oil injection with a variable ramp mixture set by throttle. Yamaha 2 stroke jet skis set about 60:1 at idle, and gradually increase the ratio to 35:1 at full throttle where upper cylinder lubrication demands are greater. (they aren't made anymore, all 4 stroke now)

Click to expand...

I'm not arguing, just clarifying. MOST remaining stroke engines are in fact weedeaters, blowers, chainsaws, etc. and are not oil injected. Oil injected 2 strokes (boat motors, snowmobiles, etc) make up a small fraction of the total 2 strokes out there.

(quoted from post at 06:00:53 06/15/18) kcm, I think you're thinking not enough FUEL.

A 40:1 mixture can be too LEAN for some 2-stroke engines that are expecting 50:1. That's worse than not enough lube, a recipe for a scored cylinder and galled piston.

Click to expand...

Doc was right. I was figuring the ratios backwards.

I don't use 2 cycle much anymore, and when I do, it's a quick 2.5 gallon mix using Stihl oil, so no real "thought" going into it. Was absolutely my mistake.

(quoted from post at 11:10:19 06/14/18) Does it really matter if you use 40:1 or 50:1? I?m working on a weedeater for a friend it says 40:1. All I have around here is 50:1. I?ll probably mix up some 40:1 just curious on opinions.

Click to expand...

It will probably run fine for test purposes. For hard work, if it's a 40-1 machine, I wouldn't depend on 50-1 mix, even the good stuff with good gas. I run the good Dolmar oil with fresh non-ethanol gas and I just don't feel comfortable running 50-1, even in saw designed for it like my Huskys and Stihls. 40-1 isn't going to hurt the saw, but 50-1 in a saw with poor seals can be a disaster.