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Old 23 October 2013, 14:01   #1
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Yamaha 50, what's the oil mix?

Hi everyone, got hold of a Yamaha 50 horse 2 stroke and not sure of the fuel mix it needs, is it a 50 to 1 or a 100 to 1. Have not seen anything specifying it on the motor.
Model is a 50DE
Any help appreciated
Thanks
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Old 23 October 2013, 14:35   #2
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Fuel Mixes

Yamaha 2 cylinder to 60hp - 100-1

Yamaha 3 cylinder to 70hp - 100-1

Yamaha 3 cylinder from 75hp and all V models were 50-1.

To complicate things the mariner/yamaha 2 cylinders usually ran at 100-1 up to 40 hp and 50-1 above, even though they were the same. Some of the 25s run on 50-1 just to make things awkward.

I am a bit grey on the 3 cyl yamaha 70, but as it had the same block and unit construction crank as the 60, I'm 99% certain it was 100-1.

If I remember the oil injection systems on yamaha were launched in 1990!!
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Old 23 October 2013, 15:15   #3
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Thanks for that RIB-Teccie, it's a 3 cylinder pre mix engine and thought the Guy I bought it from said 50-1, but not sure now as I have a memory like a sieve.
Also looking for a spare prop for this engine, not sure what the pitch or diameter is but it will be used on a 15 foot speed boat
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Old 23 October 2013, 15:41   #4
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We are having lots of prop discussions on another thread. It's time we all logged Boat, Engine, Prop & WOT RPM, it would take guesswork out of everything.

As a rule of thumb, the heavier the boat the smaller pitch you would need and the lightest or flat bottomed, would go with a higher pitch. My guess would be a standard Yammy alloy prop around 13 or 14 pitch. Use your old one if you have one and use a cheap tachometer which wraps round the plug lead to get the rpm. Then work out which prop you actually need. You may need 2 anyway if you are boarding or have a larger crew. It's always trial and error .

If you google yamaha 50D outboard prop size, this will take you to a yamaha site and all the sizes will be there to see.
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Old 23 October 2013, 16:23   #5
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When I manage to get out on the water with it and try it out Just to see what it is like with the prop that is on I will try and get a tacho to find WOT RPM. The prop looks like it has had some work done to it by the grind marks on the ally so may not be a good comparison with the markings for size and pitch on it.
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Old 24 October 2013, 14:13   #6
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One last thought. When the larger unit construction crankshaft yamaha's (above 30hp) came out in 1884, the tolerances on the pins which held them together, were not quite tight enough and if a piston picked up or over revved it was curtains and a large hole would appear through the block wall. This led to a lot of warranty claims and the thought that double oiling would help. The mercs & mariners, Johnson's and evinrudes were all 50-1 and the Suzuki's were oil injected. This led to a lot of outboard shops doubling the recommended yammie oil, which led to the piston rings getting coked up. I don't recall it ever preventing the cranks from breaking though. I suppose if anyone was really worried they could up the oil slightly but not double it up.
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Old 24 October 2013, 14:13   #7
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1984, I'm not that old!!!
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Old 24 October 2013, 15:32   #8
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Funny, I was just reading about that problem with rings getting coked and picking up.
So 100 to 1 it is
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Old 24 October 2013, 16:00   #9
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I meant picking up through overheating. It was thought that extra oil would help, but overheating has more than one cause, impeller, thermostat, mud, poly bag, weed, mounted too high, over propping or towing. Towing was a biggie because you put the engine under huge load and you only get 2500 rpm or less flat out, which is half as fast as the impeller should rotate with that load, delivering half of the water, the block also gets hot. Then you hear a loud bang, followed by some very rude words.
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