Changing Mix Ratio and Jetting

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#1
I'm considering going to a 32:1 mix ratio from 50:1 in my 2000 KTM 250exc. If I make this change will I need to adjust my jetting for this? My current jetting is a little rich, so if I need to adjust for the new fuel ratio will i need to go richer or leaner?

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Strick

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#2
Leaner. I wouldn't change anything until you ride it with the 32:1.

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Strick '99 KTM 300mxc, AMA & BRC member
 

KDXfile

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#3
Strick,
Don't you mean richer since a 32:1 mix has less fuel than a 50:1 mix ratio?
As Strick said, don't change until you test ride. If you think the jetting is rich now, at 32:1 it may be just right.

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Mark
GasGas EC200
KTM 125 Enduro
 

Strick

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#4
KDX is right. 32:1 is leaner. So, you would richen the bike (maybe). Changing ratios might correct the problems you are having now.

Sorry - it was late!

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Strick '99 KTM 300mxc, AMA & BRC member
 
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#5
32:1 is RICHER than 50:1
32 parts gas to 1 part oil
50 parts gas to 1 part oil
more gas to the same amount of oil = leaner

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#6
Since when is 32:1 leaner than 50:1 guys, come on! 32:1 is a richer fuel-oil mixture and may or may not, depending on the type of oil you are mixxing, require you to change your jetting. A high quality oil can normaly be mixed at 40:1 to 50:1 with adequate lubrication of your rod and main bearings. A petroleum base will generally require a richer mixture for equivalant lubrication. Don't get fuel-oil mixture mixxed up with fuel-air mixture as they are 2 different entities. The fuel-oil mixture is for bearing lubrication and ring seal, and the air-fuel mixture is for clean, efficient combustion without excessive temperatures in the cobustion chamber. It is very possible to get a rich looking plug reading and still be running a too lean fuel-air mixture in your combustion chamber due to an excessive amount of unburned hydrocarbons left on the plug. This comes from a too rich fuel-oil mixture. In my KTM250 I've settled on belray H1R at 50:1 with a 175main and a 42 pilot. If I am going to be hill climbing or riding sand all day I usually bump up to a 178 main. My elevation is normally 2000-2500ft. Why are you thinking of going to 32:1?


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Smokin Joe

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#7
32:1 vs 50:1 more oil to gas = richer oil ratio but effectively leans jetting due to less gas per unit volume.

Jow

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Joe Hammond
Meridian, MS
'97 KTM 250 EXC, '85 XL-600
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KDXfile

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#8
Guys,
32:1 is leaner than 50:1.
The terms "lean" or "rich" refer to fuel/air mixing NOT fuel/oil ratios.
You jet your bike to run on gasoline, not oil. It doesn't know or care how much oil is mixed in the fuel; it needs the correct fuel/air mix for an efficient combustion process.
IE, if your bike runs perfect at 32:1 and you start running 50:1, it may be too rich and require leaner jetting.

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Mark
GasGas EC200
KTM 125 Enduro
 
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#11
I understand it oils the cylinder walls but it doesn't lube the main and rod bearings. Am I missing something?

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#12
Bill in a 2-stroke the gear oil only lubercates the gears & the clutch it does not oil the main or rod bearings.The gas premix oils the top end, main & rod bearings.

I use to ride 4-strokes so this was all new to me when I made the switch

Steve F. 98 300EXC
92CR 250 sold
93XR 600 stoled

87 XL600R sold

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#13
I'm sorry, but I think you guys are wrong. Anything below the rings does not get oiled by the oil you mix in your gas. Only the cylinder walls get lubed by this oil. The crank case oil does lube the main and rod bearings. It's not pumped around like a four stroke though. These bearings are kind of sealed, sort of. If you think about it, how would the oil from the gas lubricate the main and rod bearings. I just called my local shop to verify this.



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Strick

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#14
OMG - Guys like Rich, Eric and Tuner, have to be getting a kick out of this one!

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Strick '99 KTM 300mxc, AMA & BRC member
 
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