Mikuni Needles - What do those numbers mean?

I'm still dialing in the new Mikuni VM26 on the 250. Long story short, it works best in the midrange with a 100 main and the needle in the middle. It has the best top speed with a 115 main. However, with the centered needle on the 115 main, it runs rich and bogs and sputters a certain spots on the mid-range. Right now I've got the needle on it's lowest setting with the 115, but I'm thinking there has to be a better needle profile for me. The current needle is a 5FL14. I see Pro Flo lists needles for this carb. So which of the following would yield me fatter needle with less taper, thus leaning up the mid-range:

5DL31
5DP7
5DP39
5EJ11
5EL9
5F3
5F21
5FL14
5L1
5FP17
5D5

Better yet, if someone could decipher these numbers for me, that would be great too!

Thanks,


Post edited by: abyssdncr, at: 2005/10/09 22:16

The Mikuni needles are near impossible interpret from their item number.

Here's what I know:
5DL31

5 is the carb series - so all 5's are generally interchangeable

D first taper - the earlier in the alphabet, the smaller the taper

L second taper - the earlier in the alphabet, the smaller the taper - if there isn't a second number, then the needle only has a single taper

31 a unique number not really telling anything meaningful

If you compare a 5DL31 with a 5CN7, the 5DL31 is slightly richer in the first part of the needle coming off idle, then it is less aggressive as metering the fuel for the rest of the needle range.

What you cannot determine from this is where the taper is in relation to the length of the needle, neither can you determine the needle length.

The Sudco tuning guide does give some useful charts for a limited number of these needles.

Post edited by: jeff.saunders, at: 2005/10/10 08:40

Actually, I think Jeff gives the Sudco tuning guide a bit more credit that it deserves. The numbers (badge numbers) on the jet needles are pretty hard to interpret but you will need to replace the jet needle you have with another "5" series jet needle. I suggest you give the 5DL31 a shot... this jet needle is a good compromise and was used on the 76 VM26 carbs for the KZ900 as well as many of the earlier VM24 carbs. I am not familar with ANY 5F... series jet needles but they would likely be pretty rich...

Cut and paste this for the dimensions of the Mikuni needles.
Daniel

www.sudco.com/catalog105/056-060.pdf

Thanks for the info guys, I think that should get me going in a better direction. I'll let you know how she turns out.