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Vintage Australian Outboard Runabouts => Information Wanted => Topic started by: senojn on May 13, 2019, 12:42:02 PM

Title: Fuel Mix
Post by: senojn on May 13, 2019, 12:42:02 PM
Hi all ,glad to see there are some new posters !

With SX 2 not running on the water I regularly start her two 1981 70 hp Johnsons in drums of recycling water.
Not opening her up ,  there is quite a lot of smoke in a limited area . I think the smoke is from lack of burning not wear . ;)
I recall someone suggesting that an idling motor could possibly run safely without oil in the mix ?
Any ideas as to a higher ratio (now 50:1 ) would go to idle and fast idle running.


Title: Re: Fuel Mix
Post by: MERCMAN on May 13, 2019, 05:12:58 PM
Hi mate,
Yes, your motors will probably be happy at 100:1 when idling. There are some models of Yamaha outboards that will run all day with 100:1 at WOT!

But, why risk it? Stay with 50:1 please.
The excessive smoke is probably attributed to old fuel (having low octane) not able to properly burn oil and fuel, when mixed together.

This issue won't be wear related, I promise you. Your twins are 2 stroke as you well know.. 2 strokes are quite different to 4 strokes in so many ways.. 2 strokes don't have proper oil rings on the pistons like a 4 stroke, only a ring for compression (sometimes they may have two rings).


Title: Re: Fuel Mix
Post by: senojn on May 13, 2019, 05:56:29 PM
Thanks Guy

I use 95 with everything. .

No doubt I lose track of time (fresh/freshish ) and half filling a large tank plus almost 74 ;D
Will try a smaller quantity of high octane with oil I purchased abt 20 years ago at Sussex .
It's actually a few million years older than me  ;)

Not being mechanical I didn't know the connection between rings and smoke as my many putt putt 2 strokes had two rings :o

I shall wait for a windy day -hope you can make it  :)

Do trust your new circumstances are still going well .



Title: Re: Fuel Mix
Post by: TheJollyBodger on May 15, 2019, 10:33:06 AM
just sayin' my British seagull is 10:1... i run it on 20:1. and it doesn't smoke that much. if you have ever witnessed someone put diesel in a petrol car, you will notice how much they will smoke, thats the unburnt fuel thats making the smoke. So the chances are is that you have got a weak spark in 1 cylinder, your fuel is stale, or your thermostat has had it and the motor is not getting up to operating temp, so it doesn't burn the oil in the fuel properly.

Title: Re: Fuel Mix
Post by: senojn on May 15, 2019, 07:26:55 PM
Thank you JB
I have twin motors so that probably takes out spark and thermostat .
Stale fuel is probably correct but it is interesting that your run the Seagull on half the oil .
That's what prompted my question .
Is there a risk ?


Title: Re: Fuel Mix
Post by: TheJollyBodger on May 15, 2019, 10:19:52 PM
According to saving old seagulls (S.o.S) you are perfectly fine with 25:1 (i keep it at 20:1 to keep it on the safer side) thats because the oil technology today is way better than it was when the seagull outboard motor was designed in the 30's. Same deal with my 1962 evinrude fastwin, that originally ran on 16:1 I run that on 25:1. nowadays the standard is 40:1-50:1 with needle roller bearings, and i wouldn't push them past 50:1 unless you want scored cylinders and a worn out motor.

You could have carbon buildup that is causing the improper combustion, try spraying with a spray bottle a fine mist of water metho mix into the carbys whilst they are running at mid rpm until it starts to want to die, then let it build back up again and repeat ~5 times.

Title: Re: Fuel Mix
Post by: senojn on May 17, 2019, 11:30:34 AM
Thank you JB
I am currently giving SX 2 a good clean and I found 3 brand new plugs in the cabin drawer which I had always assumed were used  :) Must be at least 25 yrs old .
I can try these in identifying the smoke problem .
Also I found a 100 metre roll of chart recorder which is part of my fish finder .
See photos of boat and barn find  ;)
The metho method I shall pass for now.

Also check new post on the fish finder .


Title: Re: Fuel Mix
Post by: senojn on May 17, 2019, 05:15:55 PM
100 metres of sonar tape is a lot isn't it . actually 10 . :-[