Maintenance & Technical > KX500 Original

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

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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.

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