Gas-Oil ratio for 2 strokes

Jeff Reardon

Jeff Reardon

Well-known member
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I run a Yamaha 2 stroke 15, and have always been very careful to mix my gas at as close to the recommended 50:1 as possible.

I made a dumb mistake. After transferring a little over half of a 2 gallon can of pre-mixed gas into the tank in the boat, I added oil to it in anticipation that I'd top off the tank. I forgot to do top it off, and instead put a a gallon of fuel that was mixed at 25:1 into my three gallon tank in the boat. Last night I ran the boat a little on the over-oiled tank and it seemed to run just fine, though I only ran about a half gallon of fuel through it.

Question: Should I just ignore my dumb mistake and go back to adding fuel mixed at 50:1, assuming that the excess oil enrichment will be gradually reduced as I add fuel at the proper ratio? Or should I instead top off the tank now with unmixed gas to kick the ratio back where it belongs?

What are the consequences of running a 3 gallon tank of ~35:1 gas:eek:il through the motor?

Gas prices being what they are, and gasoline being hard to dispose of, I am reluctant to dump the tank and start over with the right ratio.
 
Jeff-I wouldn't worry about it. One tank of gas with more oil through your motor isn't going to make much difference. Even though my Yamaha 25 calls for 100-1, I have run 50-1 through it for years on the advice of the dealer where I bought it. I have never fouled a plug, and really only use the motor for duck hunting, which probably puts only 20 hours per year on it plus or minus. You can also get an empty gas can, split the mixture, and then add gas to approach approx where you want to be. Or just do that as you run down the current mixture. You are not doing any damage to your engine.Worst thing that happens, you foul the plugs. And I doubt that will happen for the short time you will be running that mixture.
 
My Yamaha 15hp is a 2009, supposed to run 100:1, and I always run it 50:1 oil, but then add in the Yamaha ring free, stabil, Yamaha fuel stabilizer and some Sea Foam. Quite a witches brew..... When I have allowed the gas to sit for awhile, I will dump it in my truck to mix fresh for the boat motors. I will be curious what others say, but I always error on the oil side and figure maybe it will smoke a little more, but won't be lube starved.
 
Phew!

And thanks to the Duck Boat crew for confirming that my own stupidity won't hurt me in this instance.
 
one thing I would add it to check your plugs. You could get a little fowling . Clean with tooth bush and gas if it starts to fowl.


A bit off the subject. When I was a kid we would chip in $2.35 for 6 gallons of gas and a qt of oil.

The old 10 hp johnson took a quart to 6 gallons.
 
Bill Ferrar said:
When I was a kid we would chip in $2.35 for 6 gallons of gas and a qt of oil.

The old 10 hp johnson took a quart to 6 gallons.
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For comparison, I paid $7.99 for a quart of 2 stroke oil at a convenience store. Let's not talk about what I paid for ethanol free gas, but your $2.35 would not have gotten me a half gallon.

Not sure how old you are, but my motor may date to when you were a kid. :) I think it's mid 80's. I'm at least the third owner. Should check the serial number and find out.
 
I over-oil my motor all the time. Just clean the plugs now & then and you're fine
 
Pees great now!
Just have to clean the plugs every now & then so she cranks easier.
[;)]
 
Dave,

I do the same thing. A witches brew of stabil, sea foam and ethanol free gas. Fill the 6 gallon tank after the season in January to keep moisture out and then relocate the fuel in my 4 Runner just before season in October and add fresh fuel with the brew. I run a 25 four stroke on my TDB. Seems to work well.

RVZ
 
Rod VanZile said:
Dave,

I do the same thing. A witches brew of stabil, sea foam and ethanol free gas. Fill the 6 gallon tank after the season in January to keep moisture out and then relocate the fuel in my 4 Runner just before season in October and add fresh fuel with the brew. I run a 25 four stroke on my TDB. Seems to work well.

RVZ
Click to expand...

You guys who are running your old gas in your cars and trucks--are you burning gas treated with 2 stroke oil in your vehicle? Not sure why, but that seems like it could be a bad idea.

Maybe I just have nightmares about an old Subaru I drove in college that burned oil like an Iraqi war zone.
 
Yup, I dump the 2 stroke oil in my Silverado..... 4 or 5 gallons diluted with 12 to 15 gallons of 87octane, and never notice it.
 
My buddy had a 20hp that was 100 x 1 oil ratio. Was always fowling plugs and never ran really well. Found he was mixing 25 x 1, Math. Ran it on 50 x 1 and ran fine.
 
Capt Rich Geminski said:
My buddy had a 20hp that was 100 x 1 oil ratio. Was always fowling plugs and never ran really well. Found he was mixing 25 x 1, Math. Ran it on 50 x 1 and ran fine.
Click to expand...

Dang math messin' stuff up.....
 
Jeff,
the only trouble you might get with too much oil is either a fowled plug of sluggish running motor. no big deal.
the trouble you may get from not enough oil is a scorched cylinder or seized motor.
add a little gas or not. just check the plugs after the gas is burned. a fowled plug will rear its ugly head when it gets cold out. plugs are cheap insurance.
frank
 
Jeff,
As others have said, it will run fine, but watch/change plugs. My 2004's owner's manual says use 25:1 for breakin, then go to 100:1 after that. A lot of people use 50:1 as they feel better protected from corrosion and engine wear.

v/r
Bill
 
You are right. That oil harms the catalytic converter. Its one of those things that takes awhile but it harms the beads. Those things are costly.
 
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