Call me Silly - but higher Fuel Ratio = Richer right?

[mrhoney]

I know this seems academic, but I've been searching quite a bit about ratio mixes etc and there are so many hits and in reading them it's still not totally clear.

If you increase the amount of fuel in the pre-mix ratio, doesn't that make for a richer situation?  e.g. moving from 32:1 up to 40:1 - would be going richer, not leaner as I'm adding more fuel.

Rich = more gas, not more oil (from what I've read).

I have a KX500 that the previous owner ran at 32:1, just bought a YZ250 and it's at 40:1. 

Both seem to run on the rich side - especially the YZ. 

I'd like to land on a single ratio, likely the 40:1.  In doing so - should I expect it to help my KX be more lean or will it make it more rich? 

Thank you for your patience.

[Erwin8r]

You are technically correct--but in some of these circles, people refer to "oil rich" when they use the word "rich."  The higher the fuel/oil ratio, the more fuel in the charge. 

[mrhoney]

Following this link - > http://justkdx.dirtrider.net/carbtuning.html

Also supports moving to a higher ratio will make the KX more rich, not lean. 

[2-Stroke Tom]

I think you are talking about two different things. One is the ratio of gasoline to premix, and the other is the ratio of fuel to air that enters an engine.

If you tell a mechanic that a two-stroke motorcycle is running rich, they would usually assume that you mean that there is too much oil in the premix. A 40:1 ratio means 40 parts of fuel for 1 part of oil. In this case a higher ratio (40:1 is a higher ratio than 32:1) means more fuel, and this would be considered leaner. Think of it in terms of mass. If you had a gallon of 40:1 mix and a gallon of 32:1 mix, the gallon of 40:1 mix would way less (be leaner) than the same gallon of 32:1 mix.

If you're describing a four-stroke engine, desribing the combustion characterists as "running rich" would mean that the air/fuel mixuture contains too much fuel. In this case, rich = more gas.

If your talking premix, leaner means more fuel. If your talking air to fuel ratio, leaner means less fuel.

[mrhoney]

Thank you, this helps.  So this means to me that fouling a plug, moving to 40:1 from 32:1 would likely help reduce the frequency of this happening. 

Stuttering at higher throttle likely not effected by the change in ratio, but an adustment in the needle position and possibly main jet required.

[DoldGuy]

Mr Honey,

I don't think you are going to notice much if any difference between 40:1 & 32:1 ratios, especially as concerning fouling plugs. If you are fouling plugs you need to settle on a mix ratio & correct the jetting & stick to that ratio.

In my opinion a 40:1 ratio is "richer" than 32:1 as far as "jetting" is concerned as the Specific Gravity (or weight) of the mixed gas is lighter at 40:1 which the fuel is more readily to be picked up thru the jets. If you think about it for a moment what does a liter of gas weigh? Now a liter of oil? The more oil the heavier the Premix will be. If you suck a pepsi thru a straw, then a milk shake which gives more volume?

Just my $.02 worth

DoldGuy

[Polar-Bus]

I know this seems academic, but I've been searching quite a bit about ratio mixes etc and there are so many hits and in reading them it's still not totally clear.

If you increase the amount of fuel in the pre-mix ratio, doesn't that make for a richer situation?  e.g. moving from 32:1 up to 40:1 - would be going richer, not leaner as I'm adding more fuel.

Rich = more gas, not more oil (from what I've read).

I have a KX500 that the previous owner ran at 32:1, just bought a YZ250 and it's at 40:1. 

Both seem to run on the rich side - especially the YZ. 

I'd like to land on a single ratio, likely the 40:1.  In doing so - should I expect it to help my KX be more lean or will it make it more rich? 

Thank you for your patience.

 I'm no premix guru, but here's other educated comments that i've read and they do make sense. The richer the premix ratio the more oil % is preasent. The heavy oil makes for SLOWER moving fuel through the jets, which equates to leaner running condition. So vice-versa a leaner mixture allows the fuel to flow faster through the jets. To be honest 32:1 vs. 40:1 is now splitting hairs. I can't say I notice any difference except in my wallet when I run expensive oils at 32:1.   Don't take this post as law, again i'm no expert on this subject. This reasoning is typically why Kawasdaki's come jetted so pig rich from the factory, as Kawasaki assumes running 32:1, and you the owner are a pro level competition rider who will be holding the throttle WFO for 45 min..

[Hillclimb#42]

not sure if the thickness is relative to the ratio or not. I suppose in a "splitting hairs" discussion, it would be that way. If you look at your ratio cup and see the difference in 40:1 and 32:1 for 5 gallons of fuel, you'll see my point. Its not much less oil. ( maybe one ounce in 5 gallons) I think that it only makes sense to use one fuel can for both bikes. I don't think performance will be hurt or helped by changing to a happy medium. Keeping the fuel consistent will surely help tuning, but I don't think it will cure anything by itself. My understanding is that less oil is richer jetting, too. Its just not even close to going up a jet size, as far as getting a richer tune. The point was made when we all clarified richer and leaner does indeed refer to fuel to air. Oil to fuel is the oil ratio and is often mistakenly confused with the terms "rich" and "lean." Lots of debates on oil ratios' causes and affects, but i think everyone agrees to find a happy ratio with a quality oil and stick to it. If and when I have ever changed fuels, ratios or oils, I do not mix them with the old. Flush the tank and start anew, just to eliminate any adverse reactions to jetting.

I am also not an expert, but that is my opinion. Post a follow up, mr honey, so somebody in the furture has an easier decision to make, thanks.

[mrhoney]

Thank you for the responses, I'll post an update on my findings.