Do not know if this will help you or not, but here is what I understand about the jet needle ID Mikuni use.
The first number is the length series. Lets take the series 4 needle. It could be 40.00-49.99mm in length. In turn a 5 could be 50.00-59.99mm in length.
The second and sometimes third characters being letters describe the taper from the clip end to the tip in 15second (1/4th of a degree) increments. For example "B" is 30 seconds, and "E" is 1 degree, 15 seconds. Therefore a "BE" would be a taper starting out at 30 seconds (1/2 degree), followed by a second taper of 1min 15sec.
The last digit be it one or two characters is the suffix or revision number. Example. 4D3, and 4D8 are the same style needle, similar in length and taper. However the taper may begin higher up on the needle than the other. This would make a smaller tip diameter, or a shorter needle. If shims, or clip positions were incorporated on one needle it is possible that it may effectively perform like the other.
Lastly there is sometimes a number designated by OEM's and this designates the clip position. Example: 5DP3-4. However this "-#" designation is not part of the needed part number.
One last note: A suffix number has the following unknown variables between one needle and another. Exact length, Major OD, Point of begining of taper in reference to clip position. Without physically measuring them there is no way to determine these characteristics just by looking at the part number.
1977 KZ650 B1
Pods and Denco header
OLD KAW OWNERS SMILE ALOT
