Couple questions:

1) How does the premix ratio affect the bikes performance?
This is where the confusion of the term "rich/lean" begins.

• what is the affect of a higher ratio?
  
• what is the affect of a lower ratio?

2) What is the best way to try different ratios?
For example, if I fill up one gallon of 32:1 and it doesn't run well, do I dump it out and start over or try to mix in another 8:1 (existing) and bring to a total of 40:1?

The bike is a 2005 KTM 200exc. I have been told it can run anywhere from 32:1 to 80:1. I use Klotz Supertechniplate but would consider a switch if something better existed (performance or price).

Thanks.

I think experimenting is okay but you really need your jetting to be set up for each ratio. If you go with less oil and more gas your bike will run richer so you will need to compensate in your jetting. If I was you I would pick a ratio between 32:1 and 50:1 and stick with it.

Hello,
I'll give you and insite of what I have come across with my son's 2002 RM250 Suzuki. We use a synthetic oil. Castroll TTS . When we got the bike the previous owner ran it at 50:1 . So I did too. I run my 1996 WR200 at 40:1 . My son ran out of his fuel and used mine instead. He noticed a power difference for the better. Since then I have run his at 40:1. My belief is that the extra oil seals the rings better. Maybe I'm dreaming , I don't know.
My mate had a KTM 200 2005 model and he used motul Synthetic 2 stroke oil and ran it at 50:1
Rich/ lean your right.
Rich in a four stroke is more fuel. Black smoke
Rich in a 2 stroke is more oil. Blue smoke
Yet rich in 2 stroke fuel mixture means more fuel to oil ratio .

brt 426 said:

not exactly correct...:ride:

A rich fuel mixture, whether it be 2 or 4 stroke, is when there is to much fuel in the fuel to air mixture.

A rich premix on the other hand is when there is to much oil in the premix.

A rich premix will actually have a leaner air/fuel mixture than a leaner premix would.

Just wanted to clarify that for everyone.:prof: :thumbsup:

loudandproud said:

So if I want to lean out the air/fuel mix, I should try a richer premix? I'm at 40:1, so I can come down to 32:1?

I'll try this with one gallon of premix so I don't have to waste too much.

Veccster said:

No, you don't change oil ratio to compensate for jetting.

You need to pick a oil ratio then jet to it. Your jetting depends on such things as, altitude, weather conditions, heat build up, and even riding style. You need a certain amount of oil residue left in the crank area to keep the crank, rod, piston walls oiled. The oil is not there to burn it's there to lube the moving parts. You control the fuel/air mixture to give you the residue of oil needed for protection.



.

MXOldtimer said:

I'm not adjusting my ratio to COMPENSATE for jetting...I'm trying to figure out what determines the ratio. I'll jet accordingly once I have the appropriate ratio. You say I need to "pick" a ratio, but how does one just pick a ratio? What should I look for when picking a ratio?

That was the point of the thread...how does the ratio affect the bike? In other words, how do I pick the appropriate ratio? Shouldn't the ratio come before the jetting (insert chicken and egg analogy).

I came up with 40:1 based on suggestions from other KTM members. If everyone jumps off a bridge, should I?

Once I have the correct (if there is such a thing) ratio, I will jet accordingly.

Veccster said:

One important thing to consider with your bike is how your run the motor. Are you wide open alot? Do you spend alot of time barely gassing it in really tight trails. Somewhere inbetween? For a 200 I probably would not use less than for 40:1 for somewhat agressive riding. I have a 250 and I dump one .5 liter bottle of Castrol TTS into 5 gallons of gas and it works out about 37:1.

KX02 said:

Good point...I run a mix of tight technical stuff (2nd and 3rd gear below the band) with the occasional run down the road at full on WOT. I also run some shorter hills where I use the pipe in 2nd or 3rd.

Oil ratio depends on the type of oil you are running. Most of the synthetics are designed to be run at 40 or 50:1 and even higher ratios. Running them at much less than 50:1 may be a waste and will likely cut down on performance. Petroleum based oils usually require a much richer gas to oil ratio. i.e. 32:1 or so. READ the label and go by the manufacturer's recommendation on mix ratio. The manufacturer understands their oil and how it will work at different mix ratio.

All other things being equal, with proper jetting, a bike will usually run stronger with a higher gas to oil ratio, 50:1 or more, if that is what the manufacturer recommends. If you think about it, it's gas you need to get into the cylinder for power, not oil. The oil is there to lubricate. The more oil in the mix, the less gas will enter the combustion chamber, most likely resulting in less power. If you ran pure gas in a 2-stroke, it would be a rocket, until it blew up.

On a 2-stroke, it's a trade off between lubrication and power. You want max power (less oil) but you do need adequate lubrication. I have a CR500 that the previous owner ran at 40:1 with a full synthetic oil (Golden Spectro). This is their recommended ratio for severe riding conditions. I did the same for awhile. One day I decided to go to 50:1, as the recommended ratio was between 40:1 and 64:1. Wow! It's amazing how much cleaner it now runs. There was a very noticeable positive difference in performance with the leaner oil mixture.

In the case of Golden Spectro, if I was running a high revving 125cc on a motocross track where it's getting pretty well thrashed, I'd certainly consider going to a 40:1 mixture. On the CR500 used for spirited trail riding, I feel very comfortable at 50:1. The bike is just not working that hard most of the time and I'm well within Golden Spectro's recommended ratios. I've heard of people running much leaner oil ratios with full synthetics and experiencing no reliability issues.

Less oil equals more potential power, but you gotta read the label. I don't think the guy down the street, who runs everything at 30:1, knows more than the people who make the oil :ride:

OK, a good answer to my question. So it's not necessarily the performance of the engine that determines the mix ratio, it's the manufacturers recommendations. That makes sense...different oil compositions = different ratios.

Klotz says:

"Water cooled (2T) engines mix at 32:1 to 50:1"

I guess I should stick with my 40:1 mix.

gprodick said:

This is not correct at all. There are dyno charts out there to prove this. I saw a test done in a magazine about 8 or 9 years ago with an RM125 engine. They did a dyno test with it running 50:1, 40:1, 30:1, 20:1, 10:1, and 5:1 ratios. The 10:1 ratio made the most horsepower. AT 5:1 the engine began to be choked by the oil beyond what jetting could fix. the 10:1 ratio made 1.5 more horsepower than the 50:1 ratio. When chainsaw manufacturers dyno their engines they use around a 12:1 ratio to get the most power out of them. You must jet it properly.

Veccster said:

Use the bike manufacturer's recommendation. Most say 32:1 or more oil. I ran 20:1 for years with great success. I had previously ran 40:1. I always thought that cranks were discolored from the factory and that pistons should look like crap after 90-100 hours on them. WRONG! After switching I discovered that the extra oil made the bike run much cooler, and pistons looked brand new after 100 hours of racing on them. I took an old piston down to a local mechanic and he didn't believe that i had used it for more than 5 minutes.

KJ790 said:

Well, with all due respect, I'm not sure tests done 8 or 9 years ago are applicable to the current oil technology. I don't have any idea what kind of oil was being tested back then. I do agree the bike must be jetted properly and I think I stated that in my post. I probably should have gone further and noted the oil mixture can affect jetting. I may have over simplified my argument. If you can find that test, you should post it.

I've run and raced 2-strokes for years, especially back when that's about all there was to race. I've had a ton of different brands and models - Suzukis, Hondas, Kawasakis, a Montessa, etc. and some I can't remember. I've never had one seize on me or had any engine (piston, crank, etc.) failures, period. My engines have always worn very well. I've never had a 125cc, always 250cc-500cc. With petroleum oils, I would usually run about 32:1, as was recommended. Any richer just seemed to exacerbate the plug fouling issue. These were motocross bikes used predominately for racing purpose. If I was racing a 2-stroke today, and using a full synthetic oil, I'd probably mix at 40:1 and consider that safe - as per oil manufacturer recommendations. This would likely be the richest recommendation from the manufacturer.

It's true that some of the 2-stroke owner's manuals recommend a 32:1 ratio. But, make sure and read what kind of oil they are talking about. Oil is not oil is not oil. I would guess those recommendations are like other service recommendations in those manuals. That is to say, very conservative. If you hold to the recommended service schedule in any dirt bike manual, you had better have some deep pockets and not be looking to ride too often. To say that oil in general should be mixed at this or that ratio, is not correct. It depends on the type and quality of the oil, as well as the conditions of use.

Here is a great article on the topic:
http://www.bridgesto.../oilpremix6.pdf

They found almost a 4hp increase going from 30:1 to 15:1.

Most two stroke oils on the market haven't changed at all in 20 years at least. There isn't much new technology going into two stroke oils.

KJ790 said:

I agree with some of this.

I got to be part of a big discusion with a very intelligent engine builder / mechanical engineer. He to is of the "more oil, more power" philosiphy, but only with standard oils, not syntheitcs. He said with hard running engines (like shifter carts) they see power gains all the way down to about 15:1. This is because of the extra cooling the oil provides, transfering heat from the piston to the cylinder wall more efficeintly.

He didn't have a full explination for why it did not work with synthetics though. Said somewhere around the mid 20's:1 they would start to loose power, as if the oil was impeding combustion. Makes sense to me.

May I ask, which chainsaw manufacturer tests with 12:1? I'm very involved in the small engine industry, and just kind of interested.

As for not being able to change oil ratio once you pick one, pppfftttttt. I do it all the time. If I am jetted ideally for 1000 ft and 70 degrees, but doing a ride at 2000 feet and 85 degrees, I'll just add a bit more oil to help out the jetting. I hardly feel like changing jets for every other trail ride, and if I can be pretty close by tweaking my oil mixture, then why not? I stick between about 28:1 and 38:1. If I am doing a big climate or elevation change, of course I rejet. Otherwise, I just play with the oil mixture. Besides, I already spend more than enough time monkeying with the bike to piss off the old lady.

OHHHH the oil premix ratio debate LOL My sugestion STICK WITH MANUFACTURES SUGESTED RATIOS. Then you cant say anything about it.

im begining to see that the world would be better without two-smokes, "no more oil debate threads." haha j/k.

ratios are like religion to some folks, it seems that the less we talk about them, the better off we are as a community.

i use 32 or 40:1 amsoil in my 125, because i am an abusive revver, and the bike likes to rip way up in the rpms. i dont have any problems if i keep up on my top-end maintenence, with seasonly tear downs and rebuilds, and the occaisional look up the exhaust port for signs of blowby.

my advice is to keep it richer than 50:1 and you should be all set.

enjoy your new bike! :ride:

gprodick said:

This is actually the opposite of what is true. The more oil you can stuff into the cylinder the better the rings will seal and the more power you can make. With the proper jetting you can make anything run on any ratio but will it be lubricated enough. I read a study somewhere that found 16:1 was the best ratio for building power. I run 36:1 because I cant afford that much oil

I personally like the idea of sticking with the manufacturer's recommendation, or using _more_ oil if you're going to change the ratio at all. Two-strokes that use premix are already poorly lubricated by design, which is why the recommended maintenance involves frequently checking/changing the top end.

KJ790 said:

The argument that the more gas you can stuff into the cylinder, the more power you'll create seems to make sense when you think about it. However, this article proves that it isn't true. Don't believe everything you think.

Just_Ride_595 said:

Yeah, but at least there's empirical evidence out there to allow people to prove useful things about premix ratios. The same can't be said for religion, which is why you can't discuss religion with someone unless they already agree with you. :rant: