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1996 cr125 jetting

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I have a 1996 cr125 with fmf gold series fatty pipe and power core 2 silencer, Weisco pro lite piston, and a 1998-1999 cylinder. It's a 1996 bottom end with 1998-1999 top end basically. What should the Jetting be. Should it have the 1996 jetting or the 98-99 jetting. The plug is a light brown color but no white visible. The exhaust also spits out brownish/blackish goop.

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Nothing anyone suggest can be 100% accurate to your specific application.

 

With a light brown plug I'd say you're in the ballpark,

for you to isolate and fine tune each fuel circuit : pilot, needle, main jet.

 

How to read plugs: http://www.braigasen.com/howtoread.htm

 

Ambiant temperature and elevation are also tuning variables,

"perfect" jetting in 70°F weather will be too lean in 40°F weather.

Also, "racing" type premix oil will also tend to spooge more in cold weather.

 

As with any 2T engine (especialy older ones) everything must be mechanicaly sound

(reeds, compression, crank seals etc.) before any attempt is made in fine-tuning the jetting.

Edited by mlatour
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In Wisconsin it's about 30 degrees Fahrenheit and the plug comes out a light brown. It's not white and it's not a real dark brown/black. I just rebuilt the engine and it's only got 2 hours on it. Does this mean that when it gets in to the 80 degrees Fahrenheit this summer I'll have to do some jet work?

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Yes, figure every 15°F or so increase or decrease in ambiant temps requires a jet change if you want to maintain the same air/fuel ratio.

 

If you get it 'perfect' for running in 30°F temps, it will be too rich by the time ambiant temps reach 60-70°F

Figure needing to go about two steps leaner on all fuel circuits: pilot jet / needle / main jet  to get it back to 'perfect'.

 

Quite easy, once you find a 'perfect' setting for a specific temperature range,

note down all carb settings / temp and use it as a baseline.

 

If temps rise of fall more than 15-20°F from that range, you can fine tune from there.

 

Higher elevation and higher humidity level also require going leaner.

Edited by mlatour

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Not sure but I think this is for a 2004 CR125R, anyway here's an example of a jetting chart found in most service manuals.

As seen at the bottom of the chart, pretty much all OEM 'standard' (stock) jetting is based on 68°F (20°C) ambiant temps at sea level elevation.

 

IMG_0002-22.jpg

Edited by mlatour

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