Need some O'Advice!!

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calebpayne
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Post by calebpayne » 23 Jun 2012, 13:30

I am finishing my V-Haul project and just purchased a sweet little 1969 Merc40 motor. My question is as follows:

So you use higher 92 gasoline mixed with 50:1 oil for older engines.
If not, what type of gasoline should I use to mix my fuel.

Caleb Payne
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1961 AlumaCraft V-Haul
1969 Merc40

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lckstckn2smknbrls
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Post by lckstckn2smknbrls » 24 Jun 2012, 10:22

Regular 87 octane is fine.
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trueblue1970
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Post by trueblue1970 » 24 Jun 2012, 11:16

I use non ethanol

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Johny25
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Post by Johny25 » 24 Jun 2012, 11:21

^^^ Non ethanol is the only way to go with older outboards. The fuel systems and lines were not designed for ethanol.
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MrSimon
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Post by MrSimon » 26 Jun 2012, 12:30

Non-ethanol gas is preferred, but not entirely necessary. Higher octane might be better, but I've never been able to detect any difference in 20 years of bouncing back and forth (depends on what kind of mood I'm in when I fill up).

Either way, it is always a good idea (cheap and easy too) to replace the hose/bulb going from the tank to the motor as well as all the fuel hoses on the engine itself. You can replace them with lines designed to stand up to ethanol gas.
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kfa4303
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Post by kfa4303 » 26 Jun 2012, 13:43

87 octane, non-ethanol (a.k.a. Marine grade) fuel is your best bet. Using higher octane fuel is actually less than ideal for these old 2-stokes as it delays detonation ever so slightly causing combustion to occur fractionally later in the cycle thereby decreasing performance slightly. Plus, high octane didn't even exist 50 years ago when the motor was made, so it was never meant to run on it. Using the correct, factory recommended spark plugs is best as well. Lots of folks try to get the equivalence in other brands only to regret it end up getting the factory spec plugs in the end.

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Johny25
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Post by Johny25 » 26 Jun 2012, 14:43

^^Well put kfa4303 =D>
BOATS:
2002 Lowe 1467t
1988 Bluefin Sportsman 1900
1989 Spectrum 1900

MOTORS:
69' 6 hp Evinrude
71' 6 hp Johnson
85' 90 hp Evinrude
87' 9.9 hp Johnson (modified to 15hp)
88' 25 hp Johnson (modified to 30hp)
93' 120 hp Johnson

acabtp
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Post by acabtp » 27 Jun 2012, 10:03

hmm, a lot of misinformation going on... :roll:

1969... likely this motor was designed to run on leaded gasoline. they used to put lead in the gas primarily to improve its anti-knock abilities. regular leaded had an AKI of at least 89. so, you should run a gasoline that has at least an AKI (what we use for octane rating here in the US) of 89 in order to fuel it with a substance that matches the knock resistance it was designed for.

now, ethanol.

first - they say "ethanol collects water!" - yeah, it will absorb more water than straight gas, but it will take many months before this becomes a problem. so easy fix: don't mix up more than you need and leave your gas sitting around for many months.

second - they say "ethanol eats old rubber and clogs stuff up!" - yes, old rubber fuel supply parts are incompatible with and can absorb ethanol, leading them to swell and degrade. easy fix: replace the fuel lines on your motor and put a carb kit on the carb. takes $10 and 10 minutes to replace the lines with new ethanol compatible ones. carb kit might be a little more complex, but still isn't bad. (make sure the carb kit is recent production, not NOS)

i have been running E10 in all of my small engines since it came out without any problems because i replaced the lines where required and i don't let gas sit in the tanks.

so to answer the OP's question directly: 89 octane E10 should be fine, assuming you replace the old gas lines on that motor (which you should do anyway) and don't leave gas sitting in the tank (which you shouldn't do anyway)
kfa4303 wrote:Using higher octane fuel is actually less than ideal for these old 2-stokes as it delays detonation ever so slightly causing combustion to occur fractionally later in the cycle thereby decreasing performance slightly.
This is incorrect. There is no detonation in a properly running internal combustion engine.
kfa4303 wrote:Plus, high octane didn't even exist 50 years ago when the motor was made, so it was never meant to run on it.
While the outboard motor may not have been designed with a high compression ratio to take advantage of it, they did indeed have high octane gas 50+ years ago, such as the aviation gasoline rated well over 100 octane that was widely used during World War II.
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acabtp
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Post by acabtp » 27 Jun 2012, 10:07

Also, it is likely that your motor requires a mixture with significantly more oil than 50:1. Most of the two stroke outboards through the early seventies were running 24:1 mix. I would try to find an owners manual to check that to be sure before running it on 50:1.
New Project - Duranautic DN-16
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