From: tim@intrepid.gsfc.nasa.gov (Tim Seiss)
Subject: Re: Carb Jets, Needles, and Floats
Organization: Goddard Space Flight Center
Date: Wed, 16 Dec 1992 18:10:02 GMT

In article Message-ID: <1992Dec15.155125.15997@rtsg.mot.com> (Jim Dunne)
writes:
>    Let me be about the eighth guy to say Thanks Tim, for posting the
>     Keihin needle information.  If I can make a humble request though,
>     how about posting the Mikuni needle information when you have
>     time?  Let's save this info as an archive too, and I'll also try
>     to call this Carb Parts Warehouse and get my own copy.


  Some general comments about needles (taken from Carburetor Parts Warehouse
  catalog,1990 ed.):

    The needle controls the amount and mixture of fuel which is drawn in
    mid-range (1/4 - 3/4) throttle operation.  The taper of the needle
    controls the amount of fuel which is drawn. For example:  The thinner
    the taper diameter of the needle the more fuel will be drawn thus effecting
    a richer mixture.  The thicker the taper diameter of the needle the less 
    fuel can be drawn, thus effecting a leaner fuel mixture.
    
    The info that follows pertains to these carburetors:
      1) Mikuni TMX (guillotine slide) 35mm and 38mm
      2) Mikuni TM  (flat slide)       32mm, 34mm,36mm, and 38mm
      3) Mikuni VM  (round slide)      18mm --> 44mm
	
	
    There are 2 types of Mikuni needles:
    
      1) Single taper type where the needle begins its taper
	 about 1/2 way down its shank
	   
      2) Double taper type where the needle begins a slight taper
	 about 1/4 way down its shank, then starts a larger taper
	 about 1/2 way down its shank.
    

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	     _|____________________________|_    <---Richer Clip Position
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	    |________________________________|	
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	     |                              |
	     |                              |
	     |                              |
	     |                              |
	     |                              |
	     |                              |
	     |                              |
       ----->|                              |<----- O.D. 
	     |                              |       straight part
	     |                              |       (TMX models)
	     |                              |
	     |                              |
	     |                              |
	     |                              |
	     |                              |<------
	     |                              |  1st taper of
	     |                              |   double taper type
	     |                              |
       -----> \                            /<------------ 
	       \                          /
		\                        /
		 \                      /
		  \                    /
		   \                  /
		    \                /
		     \              /
        1st taper of  \            /        2nd taper of
   	single taper   \          /         double taper type
	type		\        /
			 \      /
			  \    /
		           \  /
        ------------------->\/<--------------------

	
	Both types are classified according to "series".  There are four
	"series" available.  The different series are: #4, #5, #6, #7,
	where
			
	SERIES TYPE                              APPLICATION
	-----------------------------------------------------
	  #4                                      All 18mm Carb.
	                                          22mm and 24mm Flange
								
	  #5                                      26mm - 32m Spigot
	                                          28mm - 34mm Flange
								
	  #6                                      30mm - 38mm Spigot
	  
	  #7                                      40mm and 44mm Spigot
	  
	  
	  NOTE: A Mikuni part number for a needle is a number-letter
	  combination.  The part number denotes the series type, the
	  angle of the taper, and the factory reference number.
	  
	  For Example:
	  
	    Mikuni No. 4D# (single taper type)
	     4  - series type
	     D  - angle of taper; angle increases (i.e. richens...Tim) in
	          relation to alphabetical progression.
	     3  - factory reference number.
	     
	     
	    Mikuni No. 4DG6 (double taper type)
	     4  - series type
	     D  - angle of 1st taper
	     G  - angle of 2nd taper
	     6  - factory reference number.

	     
	   For the Mikuni carbs, there's no chart shown describing what
	   angles correspond to which letter of the alphabet...

	   
	   The CPW catalog shows many needles using these designations for
	   the Mikuni TM flat slide, and Mikuni VM round slide carbs.
	   
	     Example:
	       For Mikuni TM28, TM32, and TM 34
		    5DP39
		    6DH3
		    6DH2
		    6F9
		    
		 For Mikuni TM36, TM38, TM39Pro, and TM41Pro
		    6FM46
		    6FJ40
		    6FJ41
		    6DP4
		    
	   There's too many to post for the Mikuni VM carbs...
	   	   
	   For the Mikuni TMX guillotine slide carbs, the book shows a slightly
	   different part # designation that includes the outer diameter (O.D.)
	   of the straight part of the needle shank:
	   
	    Example: 
	      For Mikuni TMX 6EJ12-55.  The numbers 55 indicate that the
		outside diameter of the neele is 2.55mm.  The smaller the O.D.
		the richer the mixture.  The larger the number, the leaner
		the mixture:
		
		  Typical Needle Jets Available:
		        6EJ12-57   Leaner   
		        6EJ12-56  		  
	   TMX 38mm   6EJ12-55   
		        6EJ12-54 
		        6EJ12-53   Richer   

		 
		        6EN11-54   Leaner   		  
	   TMX 35mm   6EN11-53   
		        6EN11-52   Richer     



Happy Tuning...

-Tim Seiss	  
	  
	  
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