# Brand new 9.9hp yamaha oil mixture question



## ILOVTOFISH (May 6, 2011)

I just bought a brand new 9.9hp 2stroke yamaha and i know it suppose to run on a 100:1 oil ratio.Here is my problem.I have heard a bunch of controversy regarding the oil mixture on what to run the mixture at when broke in.Even the guy at the marina said to run it at 50:1 after breakin because the 100:1 oil ratio scares him.Has anyone ever had a problem running a yamaha at 100:1?

I will be doing mostly wot[70%],maybe [10%] idleing and [10%]slow speed.I know the biggest thing i have heard is if you go wot you need to really run all motors at 50:1 to make sure it gets proper lubrication.I know yamaha would change the oil ratio if it were a problem but it seems most people i talk to run their motors at 50:1 so maybe thats why they never have any problems.What is really odd is the breakin ratio is 25:1 on the yamaha then run it at 100:1 after the 10hrs.It's usually half on the breakin.On mercs or any other 2stroke motor i have ran it's usually 25:1 on the breakin and then 50:1 after the breakin.Does anyone run their yamahas on 100:1?If yes any problems at all?Also how long have you ran it on the 100:1 oil ratio?

I don't want to blow this motor up so any imput would be helpful on this ,thanks


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## Deadmeat (May 6, 2011)

About all I can tell you is what's been told to me for years. Most folks say to run it at 50:1 although Yamaha recommends 100:1. I bought a 2008 Yamaha 2-stroke and run it at 50:1 and I had a 1988 Evinrude 2-stroke that I ran for 17 years at 50:1 and never had it in the shop once. But then there are folks on this website who have far more experience with motors than I'll ever have so I'll defer to them. You might take a look at some of Bassboy's posts for an answer.


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## Pappy (May 6, 2011)

Back in the late 80s OMC (Johnson and Evinrude) had a range of engines that were advertised to run on 100:1 ratio for around a year or two. What was found was that most engines were not run frequently enough to keep the engines protected during the down time. Not enough lubrication was left on the rotating parts to keep rust and corrosion from occuring. A Service Bulletin was then issued urging all dealers to inform owners to switch back to 50:1 rato for the duraton. Your Yamaha is built using the same basic materials and is exposed to the same environment so the best advice that can be given would be to run the engine on a minimum of 50:1. Additional benefits will be longer engine life due to reduced internal wear, a touch more power due mainly to better sealing, and peace of mind knowing you have internal parts that are better protected during times of non-usage. To put it another way..........I have never seen an engine fail from too much lubrication.


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## ILOVTOFISH (May 6, 2011)

Well thats great advice guys.I have heard that before about the johnsons and evinrudes.But like you said pappy it was from a lack of use that there was problems.That will never be a problem because my motor will never be in storage and the longest it will sit is a week if that.So basically i could do the 100:1 but you don't suggest it.Maybe i will just split it down the middle and do a 75:1 ratio to make sure there is more oil then they say to use,i know the reason they want less oil is for emission reasons to burn cleaner.The thing that gets me if yamaha knows this then why would they not change it to 50:1.Also how does more oil give you more power?Can you explain how that works?

I guess while i'm breaking it in i will do some more research on this debate.Maybe some more people will chime in who have run their motors on 100:1 with no problems.But very good advice so far.Thanks.


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## cincinnati (May 6, 2011)

A 100:1 oil ratio is suggested for environmental purposes only, since everything that passes through the engine is exhausted into the the water & the smoke is "unsightly." 

I'm old enough to remember when many 2 strokes ran on 30:1. Many racers & builders would have run even more oil IF the ignition would've tolerated it. 50:1 may have been the optimum for lowspeed operation w/reasonable plug life. 

If you're troubled by the smoke, want to save money on oil, or don't believe that there is a long-term mechanical benefit to a little more than a tablespoon of oil per gallon, then run 100:1.


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## ILOVTOFISH (May 6, 2011)

See i understand what your saying about the saving the environment theory with less oil.The thing is if yamaha knew their motors would have any trouble on a 100:1 ratio don't you think they would change it asap thats why i don't buy it's only for the saving the environment theory.

Why would they chance so many motors at 100:1 breaking down for so many years?They must of done a ton of research on this matter.What i will do is call them to see what there thinking is on this as it would not make any sense to me to run a machine on a oil ratio that has not been proven to work.Maybe people have just programed themselves through the years to stay at 50:1 on all 2strokes because they feel comfortable with it.Just a theory.I totally understand what you guys are saying though as it makes a ton of sense also,make sure there is more then enough lubrication to protect the machine.Thanks for the imput,good stuff so far as i have learned some good facts so far.


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## Pappy (May 6, 2011)

ILOVTOFISH said:


> See i understand what your saying about the saving the environment theory with less oil.The thing is if yamaha knew their motors would have any trouble on a 100:1 ratio don't you think they would change it asap thats why i don't buy it's only for the saving the environment theory.
> 
> Why would they chance so many motors at 100:1 breaking down for so many years?They must of done a ton of research on this matter.What i will do is call them to see what there thinking is on this as it would not make any sense to me to run a machine on a oil ratio that has not been proven to work.Maybe people have just programed themselves through the years to stay at 50:1 on all 2strokes because they feel comfortable with it.Just a theory.I totally understand what you guys are saying though as it makes a ton of sense also,make sure there is more then enough lubrication to protect the machine.Thanks for the imput,good stuff so far as i have learned some good facts so far.



There is such a thing in Corporations known as the "Marketing Dept." These dreaded people have more clout over Engineering and Manufacturing than you can ever imagine. That was the main reason for the OMC 100:1 engines and I have no doubt they played a heavy hand in the Yamaha plan as well. One thing you need to remember here is that your engine will only burn around a gallon/hour at absolute WOT so you aren't damaging the environment much by going to 50:1 are you? 
Two stroke engines will typically develop more horsepower on more oil due to better sealing internally, reduced friction internally, and better heat transfer that enables a savvy user to lean the overall mixture a little more if desired. There are many more reasons, many involve combustion changes that occur but the most significant of these is that more oil will actually reduce the amount of carbon build up both on rotating and stationary parts due to the fact that the parts will typically run below the temperature needed to "burn" the oil/fuel into carbon. Heat transfer is the main reason for this. With less carbon build up the combuston chambers and pistons retain more of their designed shape and can function at or near peak for a longer amount of time. Very common myth is that more oil creates more carbon. If you are truly interested in two strokes I would urge you to read some of Gordon Jennings works on two-stroke engines and theory. By the way, when you call Yamaha you will be talking to a person on the phone, much like yourself, that was hired because he or she has some mechanical aptitude and may have been in the Marine industry (dealership?) for awhile. They will quote you the Company line (insert "Marketing" here) as they are told. I really doubt you will be lucky enough to get ahold of a design Engineer unless you want to hit the Miami Boat show during Dealer days or happen to hit a dealership durning one of their rare appearances.


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## ILOVTOFISH (May 7, 2011)

Good stuff pappy.I guess whats the worst you will get with a little more oil,smoke.Ok i guess i will go with the 50:1 as what you say makes alot of sense.Thanks for the info.


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## Pappy (May 7, 2011)

You're welcome.


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