old outboard fuel mix

[bugeye]

Hi folks,
I've got an old Evinrude weedless three, that I'm guessing is of early sixties vintage. It's really a nice old engine, very smooth and quiet compared to most modern toy outboards. The fuel mix is 16 to 1, which I have been loyal to, but is that really necessary? I suspect that this may be similar to fiberglass boats of the era, way heavier than necessary. This is my suspicion, but don't have the courage to use less oil. Anybody have any wisdom on this? I'd love to hear someone say that they use half that amount of oil in their and haven't had problems. Rainbows are real purdy, but better in the air after a summer shower than in the water behind my skiff.

[ion barnes]

As matter of fact, I had a conversation with the local OB whiz last spring and he advised me that I could go as high as 50 - 1. His claim was that the engineers of the day were unsure of the amount of oil that was getting to the moving parts.I have a '73 9.9hp and I was sceptical, but he said to wean the OB leaner till there was no more oil on the water. I am running at 25 - 1 and its working well.

I can vouch for the fact that the plugs are burning cleaner and it seems to be much easier to start.

[Cuyahoga Chuck]

Bug,
There are three issues here.
Number one, I don't want to be responsible for frying your nice old motor. But old she is. If you need to know how old go to http://www.iboats.com/ and place a query in the Johnson-Evinrude Forum. You need the model number to get an answer.
Next, how good is the good old motor? Ever been o'hauled? If not take a compression check to get an idea of how things stand. A motor that has 80 lb or less is on the downhill side of it's existence and might need a lot of oil on the piston to maintain compression.
And, as to oil, it isn't necessarily the demands of the motor that calls the tune. Two-stroke oil chemistry has come a long way in the last 40 years. Someone who gets their hands on a pristine 40 year old motor can probably run it 50 to 1 on modern high quality 2-stroke oil. That's if it has all ball and roller bearings which don't need a lot of lube. Some really old motors have bronze or babbit bearings which need a bagfull of oil. I doubt that your three holer has any of that stuff.
As oils improved manufacturers went to 32, 50:1 and even less and I think you should be able to run at least 32:1.
Since I am a back yard mechanic I would suggest getting a second opinion from the gurus at iboats.
Charlie

[ 10-23-2005, 08:12 PM: Message edited by: Cuyahoga Chuck ]

[Canoeyawl]

I have wondered about this for years and have come up with a theory; many older two-cycle engines had plain bronze bushings for some of the rotating parts while the newer ones used roller bearings throughout. This seems to be the reasoning behind the higher concentration oil mix … I think the more roller bearings in the assembly the less oil required in the mix.
The roller type bearing has the ability to be replenished with oil continuously while the plain bronze types rely on residual oil. Most engines do have a roller bearing on the big end of the connecting rod at least, but some do not even have that, witness the seagull...
Having said that, there are different types of roller bearings, and it seems to be an evolution of sorts. Modern engines use a “needle type” that has many preassembled tiny rollers capable of efficiently trapping the oil mist. As you get more primitive this is more critical. The ancient engines actually had grease cups on the main bearings, used in conjunction with a very heavy oil mix, and this device also acted as a crankcase seal. I suspect that the newer oil formulations offer better lubricity and you may be able to switch to say 25:1 but this will also require different carburetor jetting. This is all guessing on my part and it doesn’t seem worth risking the engine. Just thinking out loud here, LOL

[Victor]

I had the same problem on a 62 Johnson 75. It smoked a lot and was hard to start, so I went from one quart oil per 6 gallons of gas = 24:1, to half that much, or 48:1, and it's done no harm. If it's true you could cut back til there's no sheen in the water, you could probably go leaner than that, but I'm not sure it would be a good idea.

[bugeye]

Hi,
thanks very much everyone!

[Andreas Jordahl Rhude]

I use 50:1 in my 1957 Johnson 35 HP outboards as well as in the 1967 Mercury 110 HP. The guy that rebuilt two of my 1957 Johnson 35 HP's swore up and down that 50:1 was the way to go.

Go to the Anique Outboard Motor Club classified forum to ask the question and to verify the year: www.aomci.org (http://www.aomci.org)