5 gal = 640 oz. Divide by 40 = 16 oz. oil. Multiply 16 * 50 =
800 oz. So you need to add 160 oz (1.25 gal) gas.

That Echo will run just fine on 50:1 with more power and less smoke although I tend to go heavier in my vintage saws because of the wider tolerances. Oil technology has really improved in the last 15 or so years.

I guess I'll catch lots of flak for this, but:
In this complicated life, I now have three buildings to store my stuff. A three bay garage, a two story storage building and a metal/post shed for most of the gardening and yard tools. No matter how I try, I cannot remember where each and every item is. I needed an automotive ammeter that I knew was around somewhere and it took me two days to find it. And I'm one of those methodical guys who thinks there should be a place for everything. My neighbor looks with wonder when he comes over to borrow a c clamp and I walk straight to it. He tells me that's not the way it is over at his place.
To get on with this, I really try to simplify storage of needed things. With that in mind, I used one brand and grade of oil for my chain saws and used it in all of them. Even though the container plainly states that this oil (Mercury) could be used for all two cycle engines; when you folks questioned that, I sent them an email and the reply gave lie to their (perhaps old) container label. So: I switched to Husqvarna two stroke (50 to 1) and use it in every two cycle engine including the ones that call for much more oil in the mix. Actually, the lawnmower and other chain saws seem to run better and haven't yet gone to that great junk pile in the sky.
Not only do I use the same brand and mix of oil in everything, I use the same gasoline in everything including the Jonsered saw that calls for hi test.
I have one five gallon can of gasoline, One 2½ gallon can of mixed gasoline, one 50 gallon drum of shell diesel oil that I use in all my vehicles. and 1 wife and 1 dog. Needless to say, one wife is all I need (or can put up with) but I could use another dog or two.
What the h___ kind of life if it when we have to spend most of our time screwing around with stuff just to mow the grass, cut down a tree, or to do the most simple things.
My advice to one and all is use the same 50 to 1 oil for everything. It works for me and I'm noted for the antique stuff I still own and use constantly so my philosophy can't be all that bad.
Jonas

A few years late but you need to add .25 gallons or 32 fluid ounces. Going from 1 over 40 to 1 over 50 you are increasing the denominator by 10 or 25% since the 40 represents the gas you need to add 25% to the gas which brings the total to 1.25 gallons since 1 gallon is already mixed you are just adding .25 gallons.

First off I don't borrow other people's expensive equipment. IMO I would just run the 40 to 1 mix. At least it won't lock up or burn up from lack of oil in case you mix it wrong. Another thing IF I had to borrow someones expensive equipment I would buy 1 gallon can and the oil he uses and mix the exact amount required. I wouldn't want to burn up a borrowed saw and have to pay for it. Which may happen anyway cause you dont' know what's been done in the pass??????

Am I the only one that switched to "one size fits all" synthetic two cycle oil? Used to have different gas cans labeled Stihl 50:1, etc. Now I mix a gallon at a time and use in everything, including "vintage." Been doing that for three years and everything is happy. Less smoke, "seems" easier starting and runs better and you go through the "new" gas faster which is important.

LOL, anyone else out there remember the "vintage" Mcculloch's, HOmelites, etc. You bought a can of 30 weight oil, used that in the chain oiler and mixed with gas? Life was simpler I guess-NOT that I want to go back to cutting wood with a 40lb. Mac!!! :-)

Ev

35.2 oz of gasoline added to 128 oz ( 1 gal.) drawn from 40 to 1 mix

Started with 640 oz ( 5 gal.) gasoline add 16 oz oil total 656 oz mixture. (40 to 1)
Draw 128 oz (1 gal.) of mixture (at 40 to 1) contains 3.2 oz of oil and 124.8 oz of gasoline.
3.2 times 50 equals 160 oz total of gasoline required, currently have 124.8 oz. need to add 35.2 oz gasoline. (Round down to one quart for a slight safety factor)

Don't be so damm cheap . Buy another gallon of fresh fuel and mix up new oil of the owners preference to his 50:1 Ratio otherwise buy your own saw .

I'm just like Jonas. Except my universal mix is a rich 32:1 . My 50:1 stuff runs fine on it. I would rather risk fouled plugs and exhaust , than scoring a cylinder

Don't know about those fancy ratio mixes. We always used a half pint of sae-30 in a gallon of gasoline, and stuff ran forever! Didn't know what "ratio" meant. Thought they just misspelled radio, and ya couldn't hear the radio when the saw was runnin'! RJ

Ok i have a gallon of 40 to 1 premix, but i need 50 to 1, how much more gas would i need to

Don't bother , just use the 40:1 . Its not that critical with today quality oils . Most professional saw users run 40:1 rather than 50:1 , which is more about epa regulations than saw performance !

Awesome answers to everything! Didn't really need an answer, my first car was a two-cycle three cylinder Saab sedan. It sounded like a very loud chainsaw. Front wheel drive, easy change thermostat to go from Summer to Winter, and one of the first front wheel drive cars around. I've been mixing oil and gas all my life. I use a 1983 Husqvarna 44. It runs great, hot knife through butter when cutting wood. The new ones use 50 to 1 and I've always used 40 to 1 with this one. So that's my two cents. Keep writing these awesome answers. This is a great website!

John , you should have been here in good old days ! lol. Welcome aboard unfortunately not a lot of activity anymore some of us old timers drop in from time to time . Should you have issues the Arborist forum is another site online that is quite active .

For 10 years Ì used 40:1 in my es-200 echo blower but yesterday messed up and added 50:1 and I can tell the motor did not like it. It bogged down, cut-out, hesitated and choked out when I released the throttle. And yes, it was the store bought, engineered mixture straight out of a new can.

GEEZE! most of these answers are just too complicated for simple people like me. Y’all are just too dang smart! Can somebody just tell me how many ounces of gas to add to a gallon of 40 to one fule to make it 50 to 1? That would be greatly appreciated. i don’t need any more people demonstrating what geniuses they are! Thanks, from just a good ’ol boy with a highschool education.