# yamaha 15hp 2 stroke 100:1 or different



## norshor (Jun 4, 2010)

I would like to know as well. I'm picking up a 15 hp Yamaha really soon myself. A buddy of mine has one, and runs Amsoil Performance 2 stroke, the same stuff that he puts in his dirtbike. I was going to run Saber https://www.amsoil.com/storefront/ato.aspx, unless I hear different.


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## Zum (Jun 5, 2010)

90% + are going to say 50:1,as well as myself.
I'm don't think synthetic oil makes a difference in ratio may be wrong though.
Might be able to get away with less oil if using the outboard everyday but not to many people are that lucky.
Longivity...50:1.


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## bAcKpAiN (Jun 5, 2010)

Follow manufacturer's specs.


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## Zum (Jun 6, 2010)

I can't beleive no one else posted on this...
I still bet most people here use a 50:1 ratio..
Trying gas/oil ratio in the search engine,I havn't but I bet something should come up.


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## Truckmechanic (Jun 6, 2010)

I run 50:1 in my 86 rude 9.9


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## bassboy1 (Jun 6, 2010)

Lets look at it this way. Back in the 80's, OMC labeled all their smaller 2 strokes as 100:1. At that point (and on to current), the technology is sophisticated enough that the motor will run forever on 100:1 without a problem. But, engines started blowing up left and right, and OMC soon regained their senses, now labeling all their 2 strokes with 50:1, and backdating that label to cover all the 100:1 motors. 

Now, if the motor could run just fine on 100:1, why did many pop? The answer has nothing to do with the motor running lean, but in fact, not even being run at all. The 100:1 did not leave enough oil residue on important parts of the motor to be stored very long, so motors that didn't get used on a weekly basis started developing minor rust and corrosion issues on vital parts, and would then spin bearings or pop upon being run again. 

Fully syn oil isn't going to make a lick of difference in this case, as no matter how good it is, if there isn't enough of it to coat the innards of the engine, it won't protect them. 

Does Yamaha have this problem? I don't know, but I do know a few people that really _know_ outboards, who run them on 50:1, especially if they aren't used on a daily or weekly basis. Were the motor mine, I would probably run it 50:1.


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## Deadmeat (Jun 7, 2010)

I've asked the same question before and just like the last time I asked it, there seems to be no consensus. I ran my 1988 30-hp Evinrude for 17 years at 100:1 and it never saw the inside of a repair shop once. But then again I was almost always on the lake at least once a week during that time. I was also religious about running a gas additive called PRI-G. Whether it had anything to do with the reliability of the motor, I don't know. My own inclination is to run it at 50:1 but the owner's manual as well as the boat dealer I bought my new Yamaha 25-hp 2-stroke from say to run it at 100:1. If the PRI-G does says what it says it does and prevents carbon deposits from building up, I can't see that 50:1 would hurt and it would give me a peace of mind that 100:1 wouldn't. While the difference between 100:1 and 50:1 is double, in the gas mixture itself it's an increase of only 1%. Would this really cause any trouble in terms of carbon deposits, etc.?


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## wasilvers (Jun 7, 2010)

I run 50:1 - which is ok for me - I start the boat and go WOT to the next fishing spot. 

So what if it fouls plugs? It's much cheaper to replace a spark plug than an engine. 

Just my .02.


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## Deadmeat (Jun 7, 2010)

If fouling a spark plug is the worst thing that can come from running 50:1, I'm in complete agreement with you. I guess the question then becomes what if any other problems can be caused by running it heavy on oil?


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## ohiobass (Aug 26, 2010)

Like above posts state, these motors were meant to run on 100:1 ratio initially, but for "safety", they now state 50:1.
I run my smaller outboards (15 hp or 9.9hp) on a 50:1, 100% synthetic, with either Seafoam or Yamaha Ring Free in every gallon of gas.
I run full throttle more than 50% of the time also, so the 50:1 is a good thing.

I also "shock" my outboards at least once a season, using Seafoam Deep Creep..

I'd probably say a 60:1 is a good compromise, and safe bet, if wanting to run a leaner oil mixture. 

The oil injection outboards have always ran a 100:1 ratio at lower rpms, and kicking to a 50:1 at higher rpms. :wink: 


8)


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## hwew (Aug 26, 2010)

My 1995 Yamaha 6hp manual said 100to1 pleasure use. And 50to1 Commercial use. Yamaha stopped printing 50to1 commercial use a few years after I purchased my engine.

Here is the way I look at it. When Yamaha made that change in the manual a few years later the 6 hp outboard parts has not changed at all. This tells me Yamaha probably was forced to change the oil ratio to pass new emissons standards. Will I ever run 100 to 1 in my outboard? NO. Why? Because I never had one engne problem with all the outboards I owned. And I put more hours on in a week than most put on in a year. I never had carbon problems at all. Of course I run a ring free additive. I only put one new set of plugs in my outboard every year.

People that run 100 to 1 and don't have problems, Hats off to you. But I will just keep wth 50to1.

50to1 will not cause problems if you maintain your engine.

Henry


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