# How To GuideOil to Gas Ratio Help!!!!!

#### Fly1

##### Member
This is a GREAT read on the subject of premix ratios.

All About 2 stroke Oil Ratios. Interesting find

I was Browsing the net and came across this, figured ive seen so much talk about oil ratios this may help some people out. I sure found it interesting.

*I did not write this, Spanky over at mx.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.

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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.

As a side note, I no longer run 26:1, I now run 32:1. I'm not a young man any more, and I just can't push as hard as I used to, so I don't need as much oil now. 32:1 is enough oil to do what is needed for me now, since I'm getting slow...

Fly

#### Waxxumus

##### Member
I have done a search and everyone has their own opinion! I wanted to try 30:1. I just want to make sure I don't mess anything up!!!!!
I dont think you understand fuel ratios.

#### Waxxumus

##### Member
I dont think you understand fuel ratios.
I dont think I understand fuel ratios.

OTP

i dont think....

#### FrenchFRI3S

##### New Member
I just use the Craftsman Full Synthetic 2-cycle oil from advanced autoparts. No problems here..

#### 45u

##### Active Member
I sure am not going to break mine it at 16-1! I build many engines for my 1/5 RC buggy and these engines are only 26 to 30cc but have a much higher RPM and much more HP and I break them in at 25-1. Being I have been building engines including but not limited to machine work on motorcycles for 45 plus years and the ONLY break in I will use is a heat cycle break in. I have many motorcycle engines I have built out there with over 100K on them still running fine and heat cycle is how I broke them all in. When you heat cycle you do not put any strain on the motor! I fire a engine up and when it is heat saturated I turn it off and let it cool all the way down. I do this 3 times before I ever put a load on it.

#### Big G

##### New Member
Hey everyone! I'm still new to the motor bike world but I have completed my first build! I love riding my motor bike. The only question I have now is after the first 2 tanks of gas what's the oil:gas ratio? The first 2 tanks I mixed 16:1. Now that the motor is broken in what oil:gas ratio should I be using? I'm wondering if there are better ratios that make the motor faster or more quiet? I don't need speed because you can only go 30mph on a motor bike here in Wisconsin. Any ratios I can use to make the motor running smoother and more quiet? Anyway, can anyone give me some insight on which ratios work better after the first 2 tanks of 16:1????? Thanks!

WickedWheelz
GO GREEN
4 oz to one gal. of gas. Use any 2 stroke oil in a china girl and your fine. The thing that makes the differance in longer life of the motor is heat. Buy and install a head with big fins, that's what really makes a huge differance. Oh and scrap the stock muffler, it builds up heat too.

S

#### sully1617

##### Guest
Hey everyone! I'm still new to the motor bike world but I have completed my first build! I love riding my motor bike. The only question I have now is after the first 2 tanks of gas what's the oil:gas ratio? The first 2 tanks I mixed 16:1. Now that the motor is broken in what oil:gas ratio should I be using? I'm wondering if there are better ratios that make the motor faster or more quiet? I don't need speed because you can only go 30mph on a motor bike here in Wisconsin. Any ratios I can use to make the motor running smoother and more quiet? Anyway, can anyone give me some insight on which ratios work better after the first 2 tanks of 16:1????? Thanks!

try 4 oz to 1 gallon of fuel. I've been running my 66cc on this mix since i broke it in about 3 years ago. it doesn't smoke really bad and it idles better. use good quality oil not the cheap sh*t. I'm using Lucas oil and love it, but i have buddies that swear by amsoil which is much more expensive and really i don't see any difference in performance between mine and theirs with one exception, one of them runs too much oil and it smokes alot.
WickedWheelz
GO GREEN

#### Big G

##### New Member
Hey everyone! I'm still new to the motor bike world but I have completed my first build! I love riding my motor bike. The only question I have now is after the first 2 tanks of gas what's the oil:gas ratio? The first 2 tanks I mixed 16:1. Now that the motor is broken in what oil:gas ratio should I be using? I'm wondering if there are better ratios that make the motor faster or more quiet? I don't need speed because you can only go 30mph on a motor bike here in Wisconsin. Any ratios I can use to make the motor running smoother and more quiet? Anyway, can anyone give me some insight on which ratios work better after the first 2 tanks of 16:1????? Thanks!

WickedWheelz
GO GREEN

#### Big G

##### New Member
4 oz to one gallon of gas after break-in. Mix it in the gas can and make sure to shake the can really well before you fuel the bike. I have used a variety of brands of oil and I have settled on the inexpensive Chevron brand two stroke oil. I have used it in 7 bikes that I have built and when I look at the cylinders after several hundred miles, the cylinders look new. I never foul a spark plug either. My goal in building the 66cc bikes was to build a big, adult sized bike (29er) that would carry me at 225 pounds with low end torque and a speed of 45 to 50 mph. Well the best that I can do is 45 but that's pretty fast on a bicycle. I have had a lot of fun building and riding the China Girls and I hope that you are having a good time too. Just remember, the motors are kind of disposable so you can't get upset if it breaks. Keep your bolts tight, your chain well adjusted and your brake pads good and you will have a heck of a lot of fun.
Big G