Trapshooters Forum banner

Status
Not open for further replies.
1 - 13 of 13 Posts

·
Registered
Joined
·
95 Posts
Discussion Starter #1
Just got an old 15 hp Johnson from my father in law. Never had an outboard before. He didn't remember the gas to oil ratio. One friend told me 50:1 another told me 25:1. So which is it?
Thanks
Sean
 

·
Registered
Joined
·
1,988 Posts
Assuming it's water cooled and at least a 1960 model run it at 50:1, You can run it 25:1 but take a case of spark plugs and a respirator with you.


Jim
 

·
Registered
Joined
·
9,975 Posts
I use Amsoil synthetic...run it 100:1 as directed..lot less smoke and runs smoother..( mine is a 140 V4 Johnson thats a 50:1 with regular oil)..It seems expensive per bottle but works out near the same
 

·
Supporting Vendor
Joined
·
9,755 Posts
Calvin, if I were you, I would stop running the 100:1 ratio on OMC products. There was a program on the late 80's to early 90's motors that they would inspect and replace the power heads if needed, remove the 100:1 ratio stickers on the sides of the motor and slap a 50:1 sticker in it's place.

50:1 it is.
 

·
Registered
Joined
·
16,534 Posts
The following is generally true: 1958 and prior used 20:1, 1959 thru 1963 used 24:1, 1964 and newer use 50:1. High performance usage (racing) requires a ratio of 25:1. New engine break-in (not DI) requires 25:1.

If it's a Maroon one better chase down the date of manufacture.

FYI 20: 1 is a quart to 5 gallons, 24:1, 6 gallons.


HM
 

·
Registered
Joined
·
2,461 Posts
In 1957, the Johnson 15 was replaced by the famous 18 (the DC-3 of outboards). If your 15 is of that vintage (pre 1957), then run 24/25:1, which is approximately 6oz oil per gallon of gasoline.

A new low profile 15 came out about 1974. It was the same physical size as a 9.9. Those motors were 50:1 ratio, which is 2.75oz oil per gallon of gasoline.

100:1 was one of a few tragic mistakes by OMC in the 1980's. Don't go to 100:1 unless you do nothing but run your engine at idle speed.

It will not hurt a 50:1 engine to run it with a 24/25:1 ratio mix, i.e., twice the oil. Perhaps if you idle all the time, you might fowl up a plug, but the plugs should quickly "burn off" clean once the throttle is opened up for a few seconds.

Mike
 

·
Registered
Joined
·
9,975 Posts
Thanks Tron...my brothers have gotten on the water with it way more than me since I got sick...looking forward to weting a line soon though
 
1 - 13 of 13 Posts
Status
Not open for further replies.
Top