# Is 50:1 really 39.4:1?

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I might be the smartest, dumb-guy or the dumbest smart-guy--I'm not sure.  Help me.

Premix ratios seem to assume that a gallon of gas weighs the same as a gallon of water...128 ounces.  In reality, gasoline is less dense than water.  For the sake of argument, the Department of Energy had a blurb that stated one gallon weighs 6.3 pounds...100.8 ounces.  So, when I mix 2.6 ounces of two-smoke oil in, I'm making a 39.4:1 ratio.  A true 50:1 ratio is about 2 ounces.

Here it comes: do two stroke oil makers/engine manufacturers factor this in?  If so, great.  If not, I'm running a fat mixture in my KTM (which it seems just fine with).

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The ratio is volume not weight

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You're mixing up volume and weight in your post anyways. A gallon is 128 fluid ounces no matter the type of liquid. A gallon of water weighs 8.3# or 133 ounces

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Density which is mass/volume.

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To the OP. Look up unit analysis. You will see the error of your ways.

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50:1 is not enough oil for a KDM.

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Will that make it squeak?

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This topic isn't worth getting triggered over.

I'm really not trying to ask a stupid question.  If it's purely a volume relationship, that's fine.  Oil and gasoline also don't have the same densities, so it must be volume.

Truly, I did not know.  Thanks everyone for your help.

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You are supposed to run 60:1 anyway, not 50:1

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Pat, that's also true-I read that in the manual as well.  Since the bike has so few hours on it, I'm running 50:1.  The jetting had the biggest change in rich/lean, so I'm not too worried about running a slightly richer mixture.  I pulled the plug the other day and it looks just fine.

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50:1 is a leaner oil mixture and carb controls air/fuel ratio. Has nothing to do with amount of oil you run

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3 hours ago, bfaucett said:

50:1 is a leaner oil mixture and carb controls air/fuel ratio. Has nothing to do with amount of oil you run

50:1 is a leaner oil mixture than.....what? In order to make a this that statement, you need a that.

32: 1 is 4 oz of oil per gallon of gas

40:1 is 3.2 oz of oil per gallon of gas

50:1 is 2.6 oz of oil per gallon of gas

60:1 is 2.13 oz of oil per gallon of gas

So if the manual says 60:1 and he goes to 50:1 he is making the bike richer in oil, and leaner in fuel. But that adjustment from 60 to 50 will have a negligible effect on fuel, but a reasonable effect on oil. I think his argument is that he wants to provide the motor with more oil to break in parts. Not that I agree with that, because the best break in is a turn it on and ride it but, his theory is I guess "sound".

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50:1 is a leaner oil mixture than.....what? In order to make a this that statement, you need a that.
32: 1 is 4 oz of oil per gallon of gas
40:1 is 3.2 oz of oil per gallon of gas
50:1 is 2.6 oz of oil per gallon of gas
60:1 is 2.13 oz of oil per gallon of gas
So if the manual says 60:1 and he goes to 50:1 he is making the bike richer in oil, and leaner in fuel. But that adjustment from 60 to 50 will have a negligible effect on fuel, but a reasonable effect on oil. I think his argument is that he wants to provide the motor with more oil to break in parts. Not that I agree with that, because the best break in is a turn it on and ride it but, his theory is I guess "sound".

Yeah I had a brain fart and was thinking in terms of fuel because of his reference to a/f

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The only correct responses are:

Yamalube 2R

32:1 for 80 / 125

40:1 for 250

Any other ratio or oil is incorrect and should result in having your bikes taken away and your nuts removed.  That is all.

Edited by redrider144
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12 minutes ago, redrider144 said:

The only correct responses are:

Yamalube 2R

32:1 for 80 / 125

40:1 for 250

Any other ratio or oil is incorrect and should result in having your bikes taken away and your nuts removed.  That is all.

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9 minutes ago, clappedoutkx said:

My 1980 PW50 was oil injected, but I do believe we used Yamalube FTW!

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34 minutes ago, redrider144 said:

The only correct responses are:

Yamalube 2R

32:1 for 80 / 125

40:1 for 250

Any other ratio or oil is incorrect and should result in having your bikes taken away and your nuts removed.  That is all.

Yamalube 2R is good stuff. Use it myself, and the bike runs tops on it.

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Ran 40:1 in my 08 as suggested by all the guys that race at my local dealer. Ran perfect. When I sold the bike it still had the same spark plug it had in 95 hrs after I bought it. Never fouled and no splooge. Thinking of running same ratio in my 17.

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This is a total hi-jack of the original posting but it hits home with me too, so I'll risk some condescension:

For the past 30 years or so I've dumped a pint (16 oz.) of Yamalube 2R into 5 gallons of premium (rec-gas the past 5 or 10 years) for a 40:1 ratio.  I've run that through 3 KTM's (86 250, 95 300, and 06 300) and I've fouled exactly 1 plug and squeeked 1 top end (totally my fault, was chasing a CRF450 down a dirt road).  So having just bought a 17 300 I was figuring on staying with my previously successful oil and ratio.  But as this is the first NEW bike I've ever had, I actually have the manual to read and there it is: 60:1.

So part of me says "it's a new motor design and KTM knows more than I do" so I'm tempted to run 60:1 but part of me says "safety first, it's a brand new motor, extra oil won't hurt, go with tradition ".  I've also thought of splitting the difference and running 50:1.  Further, Yamalube has served me well but the guy who taught me to use it in the first place is a mechanic at a KTM dealership and he now says I should run Water Pumpers to keep my Enduro Engineering USFS sparky cap from gumming up.  Seeing as the dealership he worked at (Lansing Cycle) BECAME Enduro Engineering, he should know.  So, I'm unclear on how to proceed.

Thoughts?

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Yamalube is a high quality oil. It is important that you run a high quality oil blended for use in premix for a two-stroke. Four stroke oil, and two-stroke for oil injection is different.

It really doesn't matter which brand you use. Its better to use one brand/weight so you can get used to it, so pick one and stay with it.

It also really doesn't matter what ratio you use. Use what the oil engineers at your brand of oil say. Some oil is designed for 100:1, others 60:1 or 50:1 or lots of other numbers.

I love the smell of old school Castrol R bean-oil, but its a mess to work with and the premix goes bad quickly, so you end up throwing out a lot of oil/gas.

You do have to correct the jetting when you change oil ratios. More oil means less fuel in the mixture. Or you can just run fat and be safe and give up some power.

This is seriously a case of YMMV. The internet forums are fully of heated arguments over premix and most of the folks throwing the heat have no clue what they are talking about.