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Smallest jets you ever ran in a 250

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I'm wondering what's the smallest jets you ever ran in your cr250 or 125 I currently run a 150 -48 and I still get rich stutter and plug is black not coffe

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That seems very lean.  Are you sure that you dont have a tranny side crank seal leaking oil into the crankcase.

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A few things can make you have to jet leaner to compensate for:

 

-a too high fuel level in float bowl,

 either due to mis-adjusted level or worn / damaged float & inlet valve issues

 

-worn needle jet nozzle

 some carburators have a fixed non-replaceable brass nozzle in the bottom of the venturi, it's the 'hole' where the needle slides into.

 If that orifice wears out-of-spec, the needle circuit becomes richer affecting the fuel metering from 1/4 to 3/4 throttle.

 you can try to compensate with leaner settings but likely with inconsistent fuel metering results.

 

-changing the premix ratio, say going from 32:1 to 50:1

 if the jet size is unchanged, as the reduced oil volume is now replaced by extra fuel you get a richer air/fuel ratio (rich),

 requiring leaner jetting to correct back to the proper air/fuel ratio.

 

-worn/damaged reeds or low compression/worn top-end:

 perhaps not to the extent you are experiencing but any of these issues will make the engine act somewhat 'richer' than normal,

 needless to say compensating the jetting for any of these worn components is pretty useless but many are in denial and insist on doing so...

 

Also, are your current jets genuine OEM parts for your application?

Even though they should flow equaly, you cannot really compare OEM jet sizes with theoretical equivalent sizes from aftermarket jet suppliers.

Edited by mlatour

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The stock jetting on my 83 atc 250r is 130 main 50 primary, but it is an air cooled power valveless engine

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Maybe your needle is way rich.

More to the carb than pilot/main.

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