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how to read CR250 Mikuni needle jet size

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Hey guys,

 

Could someone please explain the numbers on a needle jet for a mikuni carb?  I'm currently running a 38-73 needle but a lot of the people I talk to say I would be happier running a 38-70 needle.  I don't have a problem with going with what other recommend but I would like to understand the numbering for the needles first.  I understand the nozzle sizes, main jet and pilot jet it's just this damn needle thingamobob :)

 

Thanks a lot 

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My owners manual (CR250) has very detailed info in the optional parts section showing the different needles, rich to lean. It is in the front area of the manual. Maybe the CRF has that also.

Edited by Piney Woods

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On 6/22/2018 at 11:34 AM, cerialsledder said:

Hey guys,

 

Could someone please explain the numbers on a needle jet for a mikuni carb?  I'm currently running a 38-73 needle but a lot of the people I talk to say I would be happier running a 38-70 needle.  I don't have a problem with going with what other recommend but I would like to understand the numbering for the needles first.  I understand the nozzle sizes, main jet and pilot jet it's just this damn needle thingamobob :)

 

Thanks a lot 

38-70:
38 =Length from tip of needle to start of taper=38mm

70= Diameter of cylindrical portion of needle= 2.70 mm

 

38-73:.

38 =Length from tip of needle to start of taper=38mm

73= Diameter of cylindrical portion of needle = 2.73 mm

 

thus, the 38-73 needle is a leaner needle than the 38-70, or put it another way....

the 38-70 is going to be one big FAT RICH needle compared to a 38-73.

Nothing wrong w/ that if that's what you are after.

 

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Thank you very much for clearing that up for me. I'm hoping that running this needle with the S8 nozzle will help things out a bunch. My plugs are coming out pretty black and all I do is ride trails on my cr250r so we'll see. If not then back to the old drawing board




38-70:

38 =Length from tip of needle to start of taper=38mm



70= Diameter of cylindrical portion of needle= 2.70 mm



 



38-73:.



38 =Length from tip of needle to start of taper=38mm



73= Diameter of cylindrical portion of needle = 2.73 mm



 



thus, the 38-73 needle is a leaner needle than the 38-70, or put it another way....



the 38-70 is going to be one big FAT RICH needle compared to a 38-73.



Nothing wrong w/ that if that's what you are after.



 

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