Two-stroke mix question

Now I know that in practice it doesn?t matter a jot but every time I mix up some two-stroke fuel I agonise (very slightly) over whether it?s one part oil added to 50 parts petrol or one part oil *in* 50 parts petrol/oil mix (hence one part oil added to 49 parts of petrol)

So, does a 1:50 mixture equal 2% oil in petrol or 1.96%?

Tim

on 29/08/2019, Tim+ supposed :

Well, 1:1 would be equal parts, so 1:50 is 1.96%

Cheers

As you say, "in practice it doesn?t matter a jot", as long as you've got a bit of oil in there to provide lubrication. Better to put a little too much oil in than too little.

OTOH, 1 in 2 would be equal parts so one in 50 is 2%. I have seen 2 stroke proportions expressed either way,

Plenty of online calculators for 2T oil mix

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Ive usd 50:1 with quality oil on all my garden 2 strokes for years

I thought it was (un intuitively) the opposite?

The reason being, if you put too much oil in you will still be metering the same volume of 'fuel' (which is now diluted by oil) and so you end up running with a lean 'fuel' / air mixture?

Cheers, T i m

I?m sure there are. I was just curious as to whether others find the bald ?50 to 1? mix a little bit ambiguous.

Yes, really. What?s wrong with it?

More interested in the ?correct? answer (if such a thing exists) than more opinions.

Tim

There is no correct answer. 50:1 is only a general guide, a rule-of-thumb.

This, from

and from

and from

Indeed, actual mixtures vary a lot between different engines but it was the point about whether 50:1 = 1 part oil added to 50 parts petrol or whether

That?s already been answered (and it?s the former).

Old Seagull outboards used to run on 10:1.

Tim

My short shaft 'Forty Feather-weight' with recoil starter and long range tank used to run on that very well.

I'm not sure the environment appreciated it though. ;-(

The little Yamaha 2hp 2/ runs on 50:1 I think (might be 25:1).

The Mariner 2.5hp just needs oil in the crankcase and bevel gear.

The Yamaha M12 runs on a mix of leads and acid and is much better for the environment (at point_of_use specifically) *and* my Tinnitus. ;-)

Cheers, T i m

Tim+ expressed precisely :

No, I don't find it ambiguous 50 of one and 1 of the other, that is what it says.

It could also be interpreted to mean one fiftieth part in the final mix.

Tim

My BSA C12 used petrol to oil in the ratio 8:1.

Yes, it was four-stroke engine: it just leaked a pint of oil through the seals and rings and the bore for every gallon of petrol I put in the tank.

Nick

Well no, not really.

First of all if uyou were taught anything at school 50:1 is unambiguous

And its expressed that way because that is how we measure the mix. three shovels of sand and one shovel of cement etc.

Its only ambiguous to art students.

Tim+ submitted this idea :

Hardly, that is not how it is written. Instead of writing 50:1 it could be written as 50 parts to 1 part, or 50 measures to 1 measure.

If they meant that 50 was the total measure, they would write it as

and that has a high degree of accuracy ;-)

That would be "one in fifty" rather than "one /to/ fifty".