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9.9 Johnson 1986 - Octane vs Blend Fuel (10 % Methanol)

C

chameleon

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Octane level?
I realize the oil fuel mixture was changed back to 50:1 from the 100:1.
Further to that the full range of recommend Octane is from 86 to 91 for my motor.
When I bought my motor back in 1986 ethanol in fuel was not*part of the picture.
In my area it*now makes*up 10% of volume.

My question is with todays blended fuel which*octane is best or does it not matter?
I never gave much thought to Octane always opting for 86 because of cost then a light went off :confused: making me consider Octane and the effects of methanol on older 2 stroke outboards. Any thoughts?


Oil / Fuel Mixture

I have*found a oil/fuel mixture after years of experimenting which works best to be 75:1 for trolling.

In fact I now have two tanks in use which I mix one 75:1 for trolling and one 50:1 for high speed running.
A 11 liter tank for trolling and 22 liter tank for high speed.

Tend to run on remote lakes which requires the availability of extra fuel any ways.
This combination tends to get me thru a weekend without having to refuel.


I found this combination reduces fouling and extends plug life and run time before having to change or clean them.
In fact I have found I only need to change them at a proper interval ( yearly ) never have to clean them.
Plus I find I can get lower trolling speeds when needed.
From my research on the 100:1 issue I determined rightly or wrongly it was more of an issue with the bigger horsepowers where the problem was more an issue with mixture errors ( human and mechanical).
 
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running with 100:1 is a mistake.-----------------Picture this, an old Johnson 10 HP runs at 24:1 and uses ~ double the fuel compared to the 9.9 HP you have.-------------------Double the oil + double the fuel= lots of lubrication.---That is why there are many old 10 HP motors still running strong.--------------Do the math for 100:1 and you will see why this concept was short lived along with some of these 100:1 motors.
 
Which is some what why I don't.
However that said oils have come a long way since then todays have better lubrication properties and such.
Which is why I have settled on over the years the mixtures I now use for high speed vs trolling.
Moving from 100:1 in the first few years to now 75:1 for trolling and 50:1 for high speed . The motor has on it ( 26 years ) with a 100 plus hrs a year use. Nothing more than spark plug changes until this year which I had it tuned in a local shop more so not because it seemed to need it but because I felt it would be a good idea to prevent a breaking down in a remote place - I call it getting wiser in my years. Even then the only thing it needed was a new kill switch because the original was starting to fail . ( which was a bad design location in this model year - easy to bump)

The question still remains which I now am looking at is Octane Level vs ethanol content in todays gas vs performance.
 
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chameleon said:
Which is some what why I don't.
However that said oils have come a long way since then todays have better lubrication properties and such.
Which is why I have settled on over the years the mixtures I now use for high speed vs trolling.
Moving from 100:1 in the first few years to now 75:1 for trolling and 50:1 for high speed . The motor has on it ( 26 years ) with a 100 plus hrs a year use. Nothing more than spark plug changes until this year which I had it tuned in a local shop more so not because it seemed to need it but because I felt it would be a good idea to prevent a breaking down in a remote place - I call it getting wiser in my years. Even then the only thing it needed was a new kill switch because the original was starting to fail . ( which was a bad design location in this model year - easy to bump)

The question still remains which I now am looking at is Octane Level vs ethanol content in todays gas vs performance.
Click to expand...


I have the same question. I just read in Leroy's Ramblings that the 9.9 should use 87 octane. Any there advice out there? I've been running 93, thinking its better, but I know I should use what it is designed for.
 
Octane is not a big issue....oil and ethanol is your main concern. This is speaking from years and years of adjusting ratios and fuels. Right now, I recommend no ethanol, and high quality Amsoil Saber mixed at 100:1 in the motor that you have....I have a dozen of these from the very first in 1974....to the latter years of the series/generation. NEVER EVER damaged a motor in all these years.
The motors behind me are 1986 and always run as twin tillers...primarily for freighting in remote NW Ontario. I DONT BUY GAS IN CANADA. I import everything I use. Don't trust your petrol....I bring in clear non oxy from the states that I buy wholesale. Last 5000 liters I paid .55 a liter. Not bad...why would I buy petrol in Ontario?
 
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I remember towing my 30' boat from Florida.----Poor 429 Cadillac was pinging like crazy at times.----After first fill up in Canada the pinging was no more.------I could also return timing to normal.
 
Ha! Now your talkin' Same thing with the 500 Cad 1976 Fleetwood.....used it to tow Dad's boat up and back to Dryden. Canada seems always had better gas. At least before....don't trust it now. In fact I have one tank, (250 gallon), still decent gas.....19 years old. Flew it into camp with a fuel bladder in an Otter.
 
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