Whats he truth in terms of premix ratio?

[Stusmoke]

This is a rather sily question to some of you no doubt, nevertheless I would appreciate if someone shed some proper light on this for me. Ive heard alot of opinions out there when it comes to premix ratios you wouldnt think something like this would be so controversial. anyway what does everyone run? Ive been doing 32:1 for a few about two or two and a half tanks of fuel nowkn regular fuel nd its worki g well. but i just wanted some exra opinions. My Yz250 has TONS of bottom for a smoker and this is great for me because i want it to last as long as i can before i do a top end in it. So should i adjust my ratio? What does everyone use for the diffeent types of riding ie. woods trails motocross? thanks guys

[citabjockey]

I ran 32:1 for decades. would run mineral based oil (Belray MC3, now called S2). Ran that stuff in '70s CR125's, RM125 and RM250 (all air cooled). Ran 15+ years on a Yamaha wr500 and never did a top end job on it and when I finally did (just before selling the bike) the parts inside looked like new. I just never got into the synthetic stuff -- was just stuck in my old ways.

My new-to-me KTM was fed BelRay MC1 and I received a big jug of the stuff with the bike. I heard about guys running 50:1 back in the day with that oil. Back then I had read two stroke tuning articles by Gordon Jennings saying that you should run as much oil as your engine can stand which is why I never really trusted such a lean ratio -- despite lots of reports by friends that they do just that. So, I am running the MC1 synthetic but running it at 40:1 -- just because I am still hung up on having lots of oil in there. I think I need to switch oils because the MC1 is also pretty darn old technology and it makes a pretty big mess coming out of the pipe (at least a 40:1).

It just takes awhile to teach this old dog new tricks.

[cnrcpla]

I run 32:1 in my YZ. Kept my top end fresh for 2 years. It might have even gone longer... 

[Recovered]

golden spectro golden semi synthetic321 mixed at 40:1 with 93 octane gas in my 2002 honda cr125 stusmoke your bike will run even better if you use high octane gas because it's a high compression racing engine any race engine will run all the better with high octane gas in it

[citabjockey]

quite correct. Regular gas is a no-no in these motors. I forgot to address that -- thanks for picking it up.

golden spectro golden semi synthetic321 mixed at 40:1 with 93 octane gas in my 2002 honda cr125 stusmoke your bike will run even better if you use high octane gas because it's a high compression racing engine any race engine will run all the better with high octane gas in it

[nealy578]

I run 40:1 in my sx, Been using Putoline mx7 and motorex with pretty good results. Im just trying out some Castrol A747 as apparently its the best of the best, Im not sure as yet but time will tell. It smells awesome though!!

[2T Institute]

Truth is when you actualy test oil ratios on a dyno you get the same results as Jennings and Bell did all those years ago, MORE oil=MORE power. I don't agree with all his theories but I'll give him 9.5/10 for conducting a proper test.
Here's a test what 'spanky' did and posted on a forum.

*I did not write this, Spanky over at Motocross.com did*
 
Pre-mix 101

OK, looks like it's time for a little pre-mix 101. I don't usually get into ratio discussions, because mix ratios are like religions to most people, and they tend to be closed-minded on the subject, but I'll put in my $.02 here anyway.

There is a prevailing myth that less oil is better, and that the oil in the fuel is what lubricates the engine. Both are wrong.

*less oil is better* People think that if they have a plug fouling problem or a lot of spooge, they need to run less oil. Wrong! Both problems are caused by rich jetting, and have nothing to do with the mix ratio.

*the oil in the fuel is what lubricates the engine* The engine is lubricated by the residual oil that builds up in the crankcase. All the oil in the fuel does is replenish this oil.

The best way to determine if you are running enough oil is to check the level of the residual oil in the crankcase. If the ratio you run leaves enough residual oil in the crankcase to cover about 1/8" of the bottom of the crank wheels, then you are fine. If you don't have that much residual oil in your crankcase when you pull the top-end off, you aren't running enough oil for your riding style and conditions.

With that said, to have that amount of residual oil in the crankcase at 50:1 (a ratio made popular by magazines and oil bottles), you can't be riding very hard, or your bike is jetted richer than necessary simply to deliver enough oil. I arrived at 26:1 for my bike with my riding style because that is the amount that gives me the proper amount of residual build-up. Small-bore engines require greater oil concentrations than larger engines to achieve the proper amount of residual build-up, because they rev higher and have higher intake velocities. Along the same lines, someone that pushes the engine harder, and keeps the revs higher, also needs to use higher oil concentrations to achieve the proper residual build-up.

To understand why the residual oil is so important, you have to understand what happens to the oil in your fuel when it goes into the engine. While the oil is still suspended in the liquid gasoline, it can not lubricate anything. It has about as much lubricity at that point as straight gasoline. When the gasoline enters the engine, it evaporates, dropping the oil out of suspension. Now that the oil is free, it can lubricate the engine, but it must get to the parts to lubricate them. The way it gets to the bearings and onto the cylinder is by being thrown around as a mist by the spinning crankshaft, and the droplets are distributed by the air currents moving through the engine. Ever wonder why there are two small holes in the transfer port area of the crankcase, right over the main bearings? These are to allow some of the oil droplets being flung around inside the engine to drip down into the main bearing area.

Some of the oil eventually makes it into the combustion chamber, where it is either burned, or passes out the exhaust. If the combustion chamber temps are too low, such as in an engine that is jetted too rich, the oil doesn't burn completely. Instead, some of it hardens into deposits in the combustion chamber, on the piston, and on the power valve assembly. The rest becomes the dreaded "spooge". The key to all of this working in harmony is to jet the bike lean enough to achieve a high enough combustion chamber temperature to burn the oil, but also still be able to supply enough oil to protect the engine. If you use enough oil, you can jet the bike at it's optimum without starving the engine of oil, and have excellent power, with minimal deposits and spooge. At 50:1, you simply can't jet very lean without risking a seized engine due to oil starvation, unless you're just putt-putting around on trails without putting the engine under much load.

With the high oil concentrations that I use, I tend to get far more life from my cranks and rings than most of my friends that run leaner oil ratios. The high oil content also produces better ring sealing, so more of the combustion pressure is retained.

One small point. No one ever broke an engine by using too much oil.


_________________________________________________________________________________________________

Pre-mix ratios and power production

I have run Dyno tests on this subject. We used a Dynojet dynamometer, and used a fresh, broken in top-end for each test. We used specially calibrated jets to ensure the fuel flow was identical with each different ratio, and warmed the engine at 3000 rpm for 3 minutes before each run. Our tests were performed in the rpm range of 2500 to 9000 rpm, with the power peak of our test bike (a modifed '86 YZ 250, mine) occuring at 8750 rpm. We tested at 76 degrees F, at 65% relative humidity. We started at 10:1, and went to 100:1. Our results showed that a two-stroke engine makes its best power at 18:1. Any more oil than that, and the engine ran poorly, because we didn't have any jets rich enough to compensate for that much oil in the fuel, and the burn-characteristics of the fuel with that much oil tended to be poor. The power loss from 18:1 to 32:1 was approximately 2 percent. The loss from 18:1 to 50:1 was nearly 9 percent. On a modern 250, that can be as much as 4 horsepower. The loss from 18:1 to 100:1 was nearly 18 percent. The reason for the difference in output is simple. More oil provides a better seal between the ring and the cylinder wall.

Now, I realize that 18:1 is impractical unless you ride your engine all-out, keeping it pinned at all times. But running reasonable ratios no less than 32:1 will produce more power, and give your engine better protection, thus making it perform better for longer.

[beaner]

Edit: The above was posted as I was typing this, but I agree 100%.

The harder you run it, the more oil you need. I believe in 32-1 for my MX bikes, but in my KDX 220, which is woods only -  and I'm not good in the woods, I run a synthetic at 50-1. I know 2 people, both very fast woods riders (1 gold medal ISDE, 1 factory rider) that both believe strongly in, and use 100-1 opti. I have a 2 stroke generator. It'll run all day long at 3600 RPM, so being a light application, I'm running 75-1 in it right now.

This is the best advice for premix, IMO

http://www.maximausa.com/tech-tips/oil-migration.php

I use Maxima 927 in my RM 125 at 32-1. If I ride lightly, I get spooge like crazy. If I wring it out, I get nothing. I think that says something, and backs up Maxima's recommendations.

[tweetakt]

2012 250sx is 60:1

2003 CR250 is 40:1

I use the honda synth premix.



No problems with any motors since I've been riding.  I'm certainly not afraid to crack the throttle either.

[TotalNZ]

Yamalube 2R at 30/1 i'd run 20/1 if i could afford the oil.
The more oil the better.
And once again, exhaust spooge is nothing to do with your fuel oil ratio.

[VintageBlueSmoke]

My father preached castor oil at 50:1 and used Kendall Oil and Supreme gas (back then it was 98 octane). As I got older and he stopped riding (and tuning my bikes), I went on a wayward path of what friends and magazines told me. That lead to a lot of extra work and frustration so I started paying closer attention and taking notes. What I settled on was Silkolene and race gas  at 40:1 (not that race gas ran enough better to justify the expense, but that I was in an open class on a 125 and liked hearing the excuse they could'nt pass a 125 on a 300 because their eyes burned!). 32:1 foulded a lot of plugs. 50:1 shortened rebuild times by 1 race and was usually more wear in that time.

Now, I run whatever oil is available (Penzoil Outboard and Motorcycle Oil is in it now) and 95 octane pump gas at 40:1...or when I am lazy (like that is not?) I buy premix straight from the pump.

Yep, you heard it right. Here in the Azores, our gas stations sell premixed premix straight from the pump. I don't know the ratio or the octane level, but all my vintage bikes run just fine on it. I have not done any testing to verify wear times but it's better than my buddies CR250 fuel (32:1 Honda Lube and 95 octane)!

[ford832]

I always used 32:1 in my 125's and 40:1 in the 250's.That used to be the general recommendation as well.I lack the ability to razz the 250 like the 125 and those ratio's work well with good protection and abnormally long lasting engines in for 25 yrs now.

[metal_miracle]

I  think my ratio is 30:1

since some of my bikes need 32 and some 40.. dont want to use less and my main bearings thank me..

i have a ktm 85 that i rode  130hours whit out main bearing change. I believe it lasted that long because of  running more oil.

after hearing all the stories about sx 85

[Stusmoke]

I've put premium fuel in her this time, it was actually a mishap last time I didn't read the label at the gas pump properly haha, what an idiot! Anyway I noticed how much more punchy she is now that its running 98 octane, BEAUTIFUL! I use synthetic 32:1 cos people reckon its better for the engine, although I think I might've made the mixture a bit richer then 32:1 this time round cos I filled the fuel tank up too far and had to dribble a bit more in. No biggie Thanks for the opinions guys

[eprovenzano]

Back in the day, yes the early 70's (I know damn he's old)  I ran at 30:1 on my 1974 Honda Elisinore CR125 ... and then in my 1974 Honda Elisinore CR250.  Today, I use a full syn, and because I'm old school, I have changed the ratio to 42:1    Yes I too know of guys running at 100:1.  Good for them, they have their opinion I have mine    I've jetted my bike (KTM 300) to fit the ratio I'm running...  There's the key, jet the bike to the ratio you selected.  In the past 10 years, I've fouled one plug. (I over oiled the air filter). 

In other words, pick a ratio and brand of oil you can source locally (really they're all good), jet accordingly, and stick with it.