Yamaha 100:1?

Picked up a little two-stroke Yamaha 6hp last night. Right on the fuel hookup it says 100:1, but I seem to recall reading that 50:1 is “safe?” Thoughts on this?

I have several gallons of freshly mixed 50:1 left over from my Merc. I can dilute it to 100:1 easily enough, but if it’s not necessary it would save me a bunch of time and stinky gas hands as I’ll need to pump from tank to tank to make room for fresh gas to dilute.

50:1 should be just fine. Might smoke a touch more but if anything, it can prolong the life of the engine by running a little richer on oil. Most 100:1 is for synthetic oils, keep that in mind also.

I had the same motor. It would foul plugs with 50:1. Might have just been my motor tho. I would try 50:1.

Thanks fellas. I’m going to be trolling a bunch so I was wondering if 100:1 might be a little lean. Good to know 50:1 will be safe to try.

I’ll probably experiment with 50/75/100 and see what the motor tells me and go from there.

I think most 2 strokes are at 100:1 anyway with oil injection at idle. When idling you don’t need much oil for the bearing loads, you will just end up fouling plugs and making a mess in the motor. If it will be mostly trolling I would go with the 100:1 that the engine recommends.

Just go 75:1 done…..

Now that I think about it, you could always just dump it in your tank and top it off with the proper amount at the gas station.

I use old baby bottles to pre-measure oil and toss them in the boat. On small engines and boats like these, It’s come in handy to have only as much as you may need. Bringing the big jug and a way to measure is just a pain when you’re at the gas station or on the water, let alone storing it all in such a small boat.

At the end of the season, I take my Merc premix that is left and dump it into my Chevy truck tank. Up to 6 gal of 50:1 premix per tankful. It doesn’t even know that there is a little oil and Seafoam are in there.

Saving a few buck on your outboard fuel is not worth the possible problem it could cause while you are out on the lake.

If Yamaha recommends 100:1 that is what I would use.

djshannon wrote:

At the end of the season, I take my Merc premix that is left and dump it into my Chevy truck tank. Up to 6 gal of 50:1 premix per tankful. It doesn’t even know that there is a little oil and Seafoam are in there.

Saving a few buck on your outboard fuel is not worth the possible problem it could cause while you are out on the lake.

If Yamaha recommends 100:1 that is what I would use.

This^

My fuel from lawnmower jugs, mixed chainsaw and weed whacker jugs, etc all gets dumped into the vehicle gas tank at the end of its respective season. Motors are expensive and although gas seems expensive, it’s cheap enough that I’d rather be sure to have fresh perfectly mixed gas in everything than deal with the consequences.

If a manufacturer specifically recommends something that’s what I go with. A lot of people think they “know better” or that things “don’t matter” but in reality Yamaha has made thousands of great small outboards with years worth of testing. If it states 100:1 use 100:1. Not 50:1, not 75:1, or anything else that someone tells you “should be fine”

I appreciate the feedback guys. The way I see it there are essentially two approaches:

1. See rule, follow rule, no questions asked.
2. See rule, question rule, wonder why it was made, etc.

I might still end up using 100:1 but I’m just the type of person who wants to understand why that’s the right call. “Because they said so” just doesn’t do much for me. I’d like to know what part of the design of these motors makes them want to run with half the oil as most other comparable motors. All the anecdotal evidence suggests many people running them at 50:1 or somewhere in between with good results.

Used to have a 1994 Yamaha 40hp 2 stroke carbed engine on my old boat and ran 100:1 religiously. Trolled ALOT with it and never had a problem. I have run 50:1 in that engine because I had no other choice (Forgot to gas up before I headed to a resort) and had to buy premix at the resort. Smoked a lot more but ran. Went back to 100:1 as soon as I got home.

You can run it but would add some seafoam or Yamaha ring free.

D

Been doing some research. Apparently in the early 80’s Yamaha developed some kind of an oil recirculation system which allowed them to drop oil use by 50%, hence the 100:1 ratio. Can’t find many details.

Everything I’ve gathered says 50:1 will be fine but could foul the plugs (as Dave suggested above) and coke things up. I’m going to start with something pretty close to 100:1, and the leftover 50:1 can be saved for my snowblower.

Yamaha designed the smaller motors to use this ratio,even with infrequent use.But the more you use the motor,the better 100:1 works.

OMC did the same,but did not work well for motors with infrequent use.

Attachments:

1. 

   50-to-1-oil-mixture-without-the-residual-oil-film-achieved-by-the-ratio-rust-was-forming-within-the-engine-50-1-oil-mix-chart-litres.jpg
   

Appreciate that info. This is why I like to know the WHY. Sure the motor was stamped 100:1 — that was 28 years ago and sometimes users and manufacturers will learn things about the product after years in service. As you suggest, it didn’t work out well for some who may have ran their OMC at 100:1 even though that was the manufacturer’s suggestion when released.

Now I’m curious to know what Yamaha did right, or what OMC did wrong, to get these results.

buckybadger wrote:

<div class=”d4p-bbt-quote-title”>djshannon wrote:</div>
At the end of the season, I take my Merc premix that is left and dump it into my Chevy truck tank. Up to 6 gal of 50:1 premix per tankful. It doesn’t even know that there is a little oil and Seafoam are in there.

Saving a few buck on your outboard fuel is not worth the possible problem it could cause while you are out on the lake.

If Yamaha recommends 100:1 that is what I would use.

This^

My fuel from lawnmower jugs, mixed chainsaw and weed whacker jugs, etc all gets dumped into the vehicle gas tank at the end of its respective season. Motors are expensive and although gas seems expensive, it’s cheap enough that I’d rather be sure to have fresh perfectly mixed gas in everything than deal with the consequences.

If a manufacturer specifically recommends something that’s what I go with. A lot of people think they “know better” or that things “don’t matter” but in reality Yamaha has made thousands of great small outboards with years worth of testing. If it states 100:1 use 100:1. Not 50:1, not 75:1, or anything else that someone tells you “should be fine”

There is some irony in your advice…..

Does your truck’s owner’s manual suggest running stale 2-stroke fuel??

B-man
“There is some irony in your advice…..

Does your truck’s owner’s manual suggest running stale 2-stroke fuel??”

Yes there is some irony in my advice. My truck has a 34 gal tank. 6 gals of 50:1 in a 34 gal tank makes it about a 280:1 mix ratio.

When the pipeline company ships petroleum to the distribution depot they separate the grades from each other by 3 or more pigs (large rubber balls). The same pipeline handles all grades of refined products. As the pipeline transitions from one grade to the next it is washed by the next grade down the line. The farther the petroleum is shipped the more incidental blending occurs.

You buy fuel by volume and minimum octane level, as long as it meets those requirement you get what you paid for. There may be some diesel or some other grade of oil in your unleaded … etc.

Your average four stroke car or truck are designed to live a long life with some incidental blending of petroleum products in the tank.

I wouldn’t be afraid of some owner intended incidental blending as long as you don’t go crazy.

I have a Suzuki that is rated at 100:1 but I run at 75 and it works well. Google search this and your head will spin-so many said yes absolutely and no absolutely that I went with the split the difference group. Anyway congrats on the motor that one is hard to find.