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Old 12-06-2019, 06:44   #16
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Re: Is 100:1 gas/oil ratio safe for my 2-stroke Yamaha?

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Old 12-06-2019, 07:08   #17
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Re: Is 100:1 gas/oil ratio safe for my 2-stroke Yamaha?

Quote:
Originally Posted by Quadrille in JB View Post
Thanks in advance, I’m looking for some knowledgeable advice.
I currently have an older two-stroke 8 hp Yamaha for our 8’ Caribe RIB. The motor has a placard that says 100 to 1. Them manufacturer probably recommended this very lean ratio to pass the EPA emissions tests of the day.
The engine is in great shape and runs well so I’d hate to destroy it by running too little or too much oil in the fuel.
I’m aware from my motocross days that too much oil leans out the fuel/air mixture.
Does anyone have experience running this lean a fuel/oil mixture?
I know 50:1 was used for many years. I’m thinking of maybe 75:1 as a safer alternative to the 100:1 fuel/ oil mixture.
Any ideas from this great source of information?
Thanks
I seriously doubt the manufacturer would recommend a ratio that would do harm to the engine.

Folks that were around when we used a 50/1 ratio or higher just have a hard time adjusting to the new technology and the better oils

I had one old Johnson outboard that recommended one quart of SAE 30 to six gallons of gas which is like 25 to 1

It's like the guy(s) that think the new 4 stroke outboards that are built to run on 10% ethanol need non-ethanol fuel to run properly.

Or the guys that are still changing their vehicle's oil every 3,000 miles even though the manufacturer recommends every 7,000 - 10,000
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Old 12-06-2019, 07:40   #18
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Is 100:1 gas/oil ratio safe for my 2-stroke Yamaha?

Sometimes a manufacturer in order to meet government requirements has to recommend a service interval etc. that isnít best for the machine, itís that or stop selling it, or spend money and time designing a new machine.

Iíll give you one example, in California apparently any emissions device must last 100,000 miles on an automobile, so if you own a California Miata the timing belt service interval is 105,000 miles, cause itís mandated by the government.
Own a Miata in the other 49 states and the service interval is half that, 60,000
California belts are not special belts just government mandates replacement intervals, so California Miata owners get to enjoy being stranded on the highway more often than owners in the other States.



https://www.wsj.com/articles/SB113142264803190924
https://www.bobistheoilguy.com/forum...&Number=575480

As it became increasingly difficult for two strokes to meet emissions, one of the first and easiest things to do was to reduce the oil, it shortened engine life, but at least you could still keep selling them and make a profit.
Next of course was oil injection, which could and did vary the amount of oil widely based on engine speed / throttle opening.
Then direct injection and the Orbital injection etc.

Oils really did get better, allowing leaner mixtures, and customers liked that their boat didnít smoke as much too.
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Old 12-06-2019, 07:51   #19
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Re: Is 100:1 gas/oil ratio safe for my 2-stroke Yamaha?

Just to be safe, I always run 75:1
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Old 12-06-2019, 08:01   #20
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Re: Is 100:1 gas/oil ratio safe for my 2-stroke Yamaha?

Yep, it's probably too late for folks used to 25:1 or 50:1 ratio to accept the 100:1 recommendation even though some two stroke engines have been using that ratio since the 80's and are doing fine

More opinions on 100:1 vs 50:1 : (dated 2010)

https://www.thehulltruth.com/boating...-1-50-1-a.html
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Old 12-06-2019, 08:14   #21
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Re: Is 100:1 gas/oil ratio safe for my 2-stroke Yamaha?

Quote:
Originally Posted by Quadrille in JB View Post
Thanks in advance, Iím looking for some knowledgeable advice.
I currently have an older two-stroke 8 hp Yamaha for our 8í Caribe RIB. The motor has a placard that says 100 to 1. Them manufacturer probably recommended this very lean ratio to pass the EPA emissions tests of the day.
The engine is in great shape and runs well so Iíd hate to destroy it by running too little or too much oil in the fuel.
Iím aware from my motocross days that too much oil leans out the fuel/air mixture.
Does anyone have experience running this lean a fuel/oil mixture?
I know 50:1 was used for many years. Iím thinking of maybe 75:1 as a safer alternative to the 100:1 fuel/ oil mixture.
Any ideas from this great source of information?
Thanks
I believe that the primary emissions problem with 2-strokes is the unburned gasoline (which, yes, includes oil) which comes out of the exhaust.

Less oil also means less smoke, which is also an emissions issue, of course.

I ran a McCulloch outboard in the 60's which recommended 100:1. It blew up.
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Old 12-06-2019, 08:28   #22
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Is 100:1 gas/oil ratio safe for my 2-stroke Yamaha?

I think quality of oil and how itís used really come into it also.
If you regularly pin the throttle, then maybe you should run 50 to 1. But if you mostly putt putt around in no wake zones, and if your running a high quality oil, then probably 100 to 1 is fine.
However except for an occasional fouled plug, Iíve not seen any damage from too much oil, but Iíve seen many a seized pistol, worn cylinder walls and crankshaft bearings from too little or maybe cheap oil.
Being rich doesnít hurt, being lean may, so Iíd err to the rich side, cause in truth the mixture ratio required does vary with RPM and load.
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Old 12-06-2019, 08:45   #23
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Re: Is 100:1 gas/oil ratio safe for my 2-stroke Yamaha?

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Originally Posted by thomm225 View Post
Folks that were around when we used a 50/1 ratio or higher just have a hard time adjusting to the new technology and the better oils.
.. or an older engine. We run our '83 Suzuki 5hp on 50:1, because it's seldom used for long runs. We've had 12 years of reliable operation from it so far.

Quote:

It's like the guy(s) that think the new 4 stroke outboards that are built to run on 10% ethanol need non-ethanol fuel to run properly.
The reason for avoiding gas with ethanol isn't the running, it's that the gas with ethanol is hydrophilic (attracts water) and it just doesn't 'keep' as long as ethanol-free gas. A tank of ethanol-free gas (with oil and a shot of stabilizer) seems to stay viable in our boat tank for > 3 months. Our carb has not yet clogged up.

Quote:
Or the guys that are still changing their vehicle's oil every 3,000 miles even though the manufacturer recommends every 7,000 - 10,000
There's two reasons for changing engine oil and filter:
  • viscosity breakdown
  • dirt and contaminents
Sure, a modern oil can retain its lubricating qualities for over 10000 miles, but how fast does it get dirty?
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Old 12-06-2019, 08:53   #24
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Re: Is 100:1 gas/oil ratio safe for my 2-stroke Yamaha?

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Originally Posted by Lake-Effect View Post
.. or an older engine. We run our '83 Suzuki 5hp on 50:1, because it's seldom used for long runs. We've had 12 years of reliable operation from it so far.

The reason for avoiding gas with ethanol isn't the running, it's that the gas with ethanol is hydrophilic (attracts water) and it just doesn't 'keep' as long as ethanol-free gas. A tank of ethanol-free gas (with oil and a shot of stabilizer) seems to stay viable in our boat tank for > 3 months. Our carb has not yet clogged up.

There's two reasons for changing engine oil and filter:
  • viscosity breakdown
  • dirt and contaminents
Sure, a modern oil can retain its lubricating qualities for over 10000 miles, but how fast does it get dirty?
Most of the older engines were 25:1 or 50:1.

Like I said, I had one that called for a quart of SAE 30 motor oil to 6 gallons. It was a 1960's era Johnson 40HP Outboard

The 5 hp Mercury 4 stroke I bought new in 2011 runs fine on 10% ethanol. I use a bit of stabilizer in last fall because that gas will sit in the tanks all Winter

I burn that fuel through the engine as soon as possible in Spring. Plus I usually start the engine every two weeks all Winter

This outboard is run a lot though since it's my main auxiliary on my Bristol 27.

My other 6-8 outboards I owned were all 50:1 except the 4 stroke 55 hp Homelite Bearcat I owned in 1976. It was an early 4 stroke and was simply great on fuel economy

As far as vehicles, we are changing the oil around 6,000 - 7,000 miles give or take. (or once/year) the 2002 Jeep I drive sometimes has 242,544 miles on it and it's seems to be doing OK

The 2007 has 160,221 miles and is doing fine as well. Both use a blend not straight synthetic
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Old 12-06-2019, 09:11   #25
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Re: Is 100:1 gas/oil ratio safe for my 2-stroke Yamaha?

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Originally Posted by thomm225 View Post
The 5 hp Mercury 4 stroke I bought new in 2011 runs fine on 10% ethanol. I use a bit of stabilizer in last fall because that gas will sit in the tanks all Winter

I burn that fuel through the engine as soon as possible in Spring. Plus I usually start the engine every two weeks all Winter

Personally, I would never keep any boat (or small motor) gas over winter. Mixed or not, it goes into the truck in late fall. Truck is happy, and I buy fresh gas in the spring for the boat.


Perhaps I'm being too fussy, but the #1 problem with outboards is bad (old) gas. I've seen it often. With this regimen, I have not had gas-related problems, and the engine starts first or second pull every spring, and remains reliable for the season. YMMV, of course.
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Old 12-06-2019, 10:28   #26
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Re: Is 100:1 gas/oil ratio safe for my 2-stroke Yamaha?

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Husqvarna



I just bought a tohatsu 2 stroke 9.8HP they say 50 to 1 during break in thereafter 25 to 1
This sounds very backwards. ??
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Old 12-06-2019, 10:44   #27
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Re: Is 100:1 gas/oil ratio safe for my 2-stroke Yamaha?

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Originally Posted by Lake-Effect View Post
Personally, I would never keep any boat (or small motor) gas over winter. Mixed or not, it goes into the truck in late fall. Truck is happy, and I buy fresh gas in the spring for the boat.


Perhaps I'm being too fussy, but the #1 problem with outboards is bad (old) gas. I've seen it often. With this regimen, I have not had gas-related problems, and the engine starts first or second pull every spring, and remains reliable for the season. YMMV, of course.
That's probably a good idea but my 3 gallon tank is the normal external type and the gas doesn't easily pour out so I use it up the following Spring. The last 4 -5 years, I've also left the fuel in my 2.5 gallon tank over the Winter as well. Many times they are about half full. Plus the onboard integral 40 oz tank

The stabilizer is good for 6 months it says. I use Stabil

well, this ad says it's keeps fuel fresh for 24 months, but the most I've had old gas and used it in the outboard is about 6 months.

https://www.goldeagle.com/product/st...el-stabilizer/
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Old 12-06-2019, 10:45   #28
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Re: Is 100:1 gas/oil ratio safe for my 2-stroke Yamaha?

Personally I'd run it at 50:1 or 75:1 etc. My 15 hp destroyed the main bearings at 100:1 albeit after years of use.
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Old 12-06-2019, 14:58   #29
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Re: Is 100:1 gas/oil ratio safe for my 2-stroke Yamaha?

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This sounds very backwards. ??

Correct, that is backwards. Iím looking at p.26 of the Tohatsu M6-9.8B 2017 manual and it shows during break-in 25:1 and after break-in 50:1.

We were having trouble with plug fouling trouble recently and the service guy suggested we use 100:1. That seems like not a lot so perhaps 75:1?
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Old 12-06-2019, 15:26   #30
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Re: Is 100:1 gas/oil ratio safe for my 2-stroke Yamaha?

I’ve just picked up a mint Yamaha 5hp. Previous owner had been using it at 50:1, smoking like the proverbial.
I going 75:1 an nothing for luck!
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