YZ250 Mix Ratios Question


35 replies to this topic
  • LemonDrizzle

Posted June 06, 2010 - 07:59 PM

#1

Before I get too far and in order to ward off the flaming, I'm pretty new to 2 strokes. That being said, I'm trying to understand why the popular oil/fuel ratio seems to be around 40:1 when Yamaha calls for 30:1 or 32:1 depending on what year you have. I didn't bother to ask the guy I bought my '00 YZ250 from what he was running because I knew the first thing I was buying was a service manual so at the time it didn't matter to me, but after trolling TT it seems that most people like 40:1 rather then the stock mix ratio. Is this just mainly to get that little bit of extra zip out of the bike, and if so, won't the lack of oil harm the engine? I realize that we are only talking about a minimal amount of oil but, nevertheless, I gotta know whyyyyyyyyyyy!:thumbsup:

  • 7thirtyseven

Posted June 06, 2010 - 08:44 PM

#2

Two trains of thought here on that one, 1. Mix at yamahas recommendation 2. Mix at oil manufacturers recommendation ( which can be as high as 100:1). For what it's worth I've mixed 50:1 with my oil of choice and have yet to have an issue, and yes 50:1 was an "arbitrary" choice on my part. In short for us hacks it's not that much of an issue, or atleast far less of an issue than making sure your not sucking unwanted junk into that cylinder.., If it makes you feel better I've run my bike at 50:1 for five yrs religiously measuring high quality oil, my riding buddy far more mechanically attuned fills his tank with premium, pours chainsaw mixoil by guestimate, shakes his bike to mix, and rides.

  • chadzu

Posted June 07, 2010 - 03:39 AM

#3

Why? My best guess is that after paying $10 for 12.8 oz. of oil 50-1 is all they can afford.
I pay $11 for a gallon of oil and happilly mix at 30-1.
This debate is as old as time, and it still hasn't been settled. Which leads me to believe that it doesn't really matter. Be consistant with what works for you and jet accordingly.

  • djmamayek

Posted June 07, 2010 - 06:45 AM

#4

If you do the searches, there is evidence on this forum that a "richer" gas oil mixture in a properly tuned bike makes more power.

My bike makes plenty of power, so I am happy to mix at 32:1... Bike runs great with stock jetting @ 1000ft at 32:1, so why change a good thing?

  • jwherb

Posted June 07, 2010 - 07:20 AM

#5

I've not read anything to suggest you shouldn't mix at 32:1.

  • YamaLink

Posted June 07, 2010 - 07:55 AM

#6

I've been mixing 32:1 since a kid with great results. Yeah, it's a tad rich in some elevations, but I never have to think "hmmm, wonder if it's gonna....." puke. Never seized a bike in my life.

Not saying to do 32:1. But for me and my disdain of tearing apart engines it works.

  • Fliip

Posted June 07, 2010 - 09:22 AM

#7

Just run 32:1... Its better for your bike, makes your bike run better than 40:1, and there is no reason to put less oil in it.

  • sykal

Posted June 07, 2010 - 10:26 AM

#8

I've been mixing 32:1 since a kid with great results. Yeah, it's a tad rich in some elevations, but I never have to think "hmmm, wonder if it's gonna....." puke. Never seized a bike in my life.

Not saying to do 32:1. But for me and my disdain of tearing apart engines it works.


40:1 versus 32:1 isn't going to make your bike seize, lol
running 40:1 is actually more gas, so it has more of a cooling effect than anything.

its such a small difference its laughable

with that said, at the end of the day, it's what your bike is jetted for that really counts.

if your bike is jetted for 50:1, its going to run better than a bike not properly jetted, running 32:1.

i run 40:1 fyi

  • sykal

Posted June 07, 2010 - 10:28 AM

#9

Just run 32:1... Its better for your bike, makes your bike run better than 40:1, and there is no reason to put less oil in it.


debatable.
it depends what your jetted for.

  • DLHamblin

Posted June 07, 2010 - 11:18 AM

#10

Before I get too far and in order to ward off the flaming, I'm pretty new to 2 strokes. That being said, I'm trying to understand why the popular oil/fuel ratio seems to be around 40:1 when Yamaha calls for 30:1 or 32:1 depending on what year you have. I didn't bother to ask the guy I bought my '00 YZ250 from what he was running because I knew the first thing I was buying was a service manual so at the time it didn't matter to me, but after trolling TT it seems that most people like 40:1 rather then the stock mix ratio. Is this just mainly to get that little bit of extra zip out of the bike, and if so, won't the lack of oil harm the engine? I realize that we are only talking about a minimal amount of oil but, nevertheless, I gotta know whyyyyyyyyyyy!:thumbsup:


I run 32:1 in my '06 YZ250 and my son's 2008 YZ125. You could run 20:1 as long as you jet accordingly.

  • Fliip

Posted June 07, 2010 - 12:16 PM

#11

debatable.
it depends what your jetted for.


If your bike is jetted perfectly for 32:1, and you are running 32:1, it will run better than if you are jetted for 40:1 and you are running 40:1.

  • kan3

Posted June 07, 2010 - 12:30 PM

#12

If your bike is jetted perfectly for 32:1, and you are running 32:1, it will run better than if you are jetted for 40:1 and you are running 40:1.


Can you please provide some recent factory, laboratory, or scientific information that draws the conclusion that all 2 strokes run better on 32:1 vs 40:1 with proper jetting. I'd be interested in reading it.

  • Fliip

Posted June 07, 2010 - 12:34 PM

#13

Can you please provide some recent factory, laboratory, or scientific information that draws the conclusion that all 2 strokes run better on 32:1 vs 40:1 with proper jetting. I'd be interested in reading it.


Well, I don't have the scientific information, but I'm sure someone here does. It was proven that bikes run better the more oil you put in them, down to 16:1.

Edited by Fliip, June 07, 2010 - 05:33 PM.


  • sykal

Posted June 07, 2010 - 12:50 PM

#14

If your bike is jetted perfectly for 32:1, and you are running 32:1, it will run better than if you are jetted for 40:1 and you are running 40:1.


lol....what do you mean 'runs better' exactly?

stronger? more reliable? what?
you realize not any pro-racer runs 32:1 right? they're usually upwards of 50:1.

are you aware of what can happen with running too much oil, not enough fuel?
(honest question, not trying to insult you)

  • shrubitup

Posted June 07, 2010 - 04:16 PM

#15

Depending on the RPM that your bike will see is the answer for lubrication needs. Ever wonder why some manufacturers (maxima) list that 125s should be 32:1, 250s 40:1 and 500s 50:1? It could be that as displacement increases redline decreases at least in two stroke MX bikes. Less revs means less need for oil.

32:1 is designed to protect the motor under full load wide open assuming jetting is good for the temp/elevation/anticipated load.

Running too much oil typically results in the motor running too hot because it's not getting enough fuel to cool down the combustion - given your jetting on that day. On a hot day I will be particularly careful of the mix ratio such that it matches what I'm expecting both in load, temp, and elevation.

:thumbsup:

Eh, what Maxima said:

CONCLUSIONS

* Many engines are over-lubricated at idle, sufficiently lubed at half throttle, and marginally lubed at full throttle. At full throttle for long periods of time, severe engine damage may result from insufficient lubrication.
* As the engine size decreases and RPM's increase, oil migration times decrease dramatically.
* Oil moves through and around internal engine components at various rates.
* Oil retention on major engine components (after engine is stopped) decreases as RPM's increase.

Recreational MotoCross / Enduro / X-Country Road Racing / Flat Track / TT
50 - 125cc 50-60:1 25-32:1 20-25:1
125 - 250cc 50-60:1 32-40:1 20-32:1
250cc + 50-60:1 40:1 25-32:1

Maxima Recommends: Oil/gas ratio must vary according to anticipated use:

* Many lubricant producers recommend the same gas/oil ratio for all types of riding and racing. Maxima feels this approach is too general, and urges motorcycle owners to make their decisions based on the above research.
* All of the above measurements are approximations, and should not be considered 100% accurate. They are meant to provide the browser with a basic understanding of two-cycle engine lubrication characteristics.


Edited by shrubitup, June 07, 2010 - 08:05 PM.


  • Fliip

Posted June 07, 2010 - 05:27 PM

#16

http://www.dansmc.com/2stroke_oil.htm
http://www.motoredbi...?t=21427&page=3

Edited by Fliip, June 07, 2010 - 06:17 PM.


  • KX02

Posted June 07, 2010 - 06:05 PM

#17

Generally I find that the more agressive you ride the more oil you can/should use.

http://www.maximausa...l-migration.php

  • LemonDrizzle

Posted June 07, 2010 - 06:08 PM

#18

I appreciate all of the insight. Lol, this looks like one of those threads about which oil is the best to run in your tranny. I have been running the factory mix, 30:1, since I got my bike and it seems to run well, at least that's what the spark plug indicates, so I will probably continue to use the factory mix. I ride for fun mostly and am not trying to beat anyone out on any holeshots so I'm happy with 30:1 and feel more comfortable with it. I may try 32:1 but that's about as lean as I would go. Thanks again.:thumbsup:

  • DLHamblin

Posted June 08, 2010 - 05:31 AM

#19

lol....what do you mean 'runs better' exactly?

stronger? more reliable? what?
you realize not any pro-racer runs 32:1 right? they're usually upwards of 50:1.

are you aware of what can happen with running too much oil, not enough fuel?
(honest question, not trying to insult you)


The data came from a series of tests that was done back in the late 70's or early '80s by Gordon Jennings (of then Cycle World). Somewhere I had a copy if I can find it. They found a 2-stroke made its highest power at 16:1 (properly jetted).

The reason most pro's run 50:1 is one side affect of more oil is it lowers the effective octane rating of the pre-mix. I know most of the factory YZ250's were running 50:1 for that reason. They were willing to trade some ring life (they got fresh top ends each week anyhow) to preserve the octane rating the modified motors needed.

I run 32:1 as I don't need that exta bit and my opinion is you will never hurt a motor by running with some extra oil (and jetting accordingly of course).

  • DLHamblin

Posted June 08, 2010 - 05:44 AM

#20

I found a link, not the best quality for the pictures but text is totally readable. Its aninteresting article
http://www.bridgesto.../oilpremix6.pdf





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