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Discontinued Mikuni needles

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I'm trying to order a couple slightly leaner needles for my 2002 cr250 now that the weather is getting warmer and the bike is running rich, but the two I need are no longer available! They are: 

16233-KZ3-L22 (6BEY31-74)

16234-KZ3-L22 (6BEY31-75)

What are you supposed to do in this situation?! I'm not dishing out $220 for a Keihin when this one works fine!

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gonna have to send many emails to dealers all over, deal with the carb as is, go Keihin/Lectron or JD Jetting... such is life with Honda 2 strokes these days.

 

- could also do a crapload of research and match up Mikuni needles and their dimensions versus the Honda needles or get a Mikuni from a late model Honda that so many throw away as paper weights.

Edited by DEMI
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25 minutes ago, DEMI said:

gonna have to send many emails to dealers all over, deal with the carb as is, go Keihin/Lectron or JD Jetting. .. such is life with Honda 2 strokes these days.

 

- could also do a crapload of research and match up Mikuni needles and their dimensions versus the Honda needles or get a Mikuni from a late model Honda that so many throw away as paper weights.

Are you saying I could find the same needles but disguised under different part numbers under a different brand? Are these needles not specifically made for each brand/bike?

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14 minutes ago, md30 said:

Are you saying I could find the same needles but disguised under different part numbers under a different brand? Are these needles not specifically made for each brand/bike?

a lot of mikuni needles are very similar in dimension to say OEM Honda needles... Keihin as well. But going this route requires a good bit of  time to measure, compare, etc. Somebody may have much of this info handy.

Edited by DEMI
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15 minutes ago, Keith72 said:

What needle are you running now? 6BEY30-74? Have you tried an s-8 or s-7 needle jet? What is your other jetting?

Yes exactly. I'm currently running stock jetting (32.5/380), which has been pretty good over the winter, but with a spike in the temperature on a recent ride the bike was running so rich and spewing spooge from a freshly-packed tail pipe. Honestly I'm not familiar with the s-8 or s-7 needles you mentioned.

02 jetting.jpeg

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31 minutes ago, Keith72 said:

What needle are you running now? 6BEY30-74? Have you tried an s-8 or s-7 needle jet? What is your other jetting?

^^This^^  He beat me to it.   The mikuni will run much better with a leaner air nozzle like an S7 or S8 depending on conditions.  The oem nozzle in the 02-03 CR250r's tmx mikuni came with an S9 which I felt was to rich from the factory.  When JD sold the original kits for the 02-03 models they use to come with an S4 with his needles.  I purchased one of his kits back in 2004 that came with that nozzle he has since then redesigned his needles to work with the oem S9 from my understanding.    

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+1, guys are refering to the needle jet (nozzle), not the jet needle. Most went down at least 2 sizes. 

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Is the needle jet the same as the holder which the main jet screws onto? I didn't realize those came in different sizes. I'll try the leaner ones, thanks for the tip. Where do you guys get them, ebay? This should work, yea? http://www.ebay.com/itm/Mikuni-Needle-Jets-for-TMX-Mount-Carbs-VM36-38mm-784-13005-S-7-/321925738400?hash=item4af444efa0:g:L58AAOSwB09YEBEV&vxp=mtr

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Yes the main jet holder. It should also be threaded. The one in your link doesn't look correct. I ran an s 8 with a 380 main and the needle I mentioned earlier. And a 30 pilot jet. Others ran an s 7 with good results.

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56 minutes ago, Keith72 said:

Check pro circuit 's Jetting guide. Looks like it has a part number for the needle jet

Good advice, this is what they recommend:

"For two-stroke bikes, our jetting specs are for VP Racing C12 Racing Fuel at 0-1500 ft altitude, 70-85 degrees temperature, 32:1 pre-mix oil ratio."

               main          pilot                needle             clip position    air screw     nozzle

Stock:       380         32.5               6BEY30-74              2nd          1.5              S-9  

PC:           380         32.5               6BEY30-74              3rd           1.5              S-8 (part number: 3TC-14141-S)

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Maybe this will help explain some of the Mikuni needle codes.

 

Example of Honda cr250 Needle (6BEY31-74):
6 = Series 6 needle
BFY = Triple tapered: B / E / Y
1st taper = B (30sec = 0.5 deg)
2nd taper = E (1min 15sec = 1.5 deg)
3rd taper = Y (6min 15sec = 6.25 deg)
30 / 31 = Standard / 0.5 clip Richer 
-71 / -72 / -73 etc...= Needle Straight Diameter (OD) = 2.71mm (1 step richer) / 2.72mm (standard) / 2.73mm (1 step leaner)

Example of the Yamaha YZ 125 Needle (6BFY42-74):
6 = Series 6 needle
BFY = triple tapered: B/ F/ Y
1st taper = B (30sec = 0.5 deg)
2nd taper = F (1 min 30 sec = 1.5 deg)

3rd taper =Y (6min 15sec =6.25 deg)


-42 / -43 / -44 = STD/ 0.5 clip richer / 1 clip richer 

The way Mikuni Needle numberings work is:

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 15 second (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. For this reason we sometimes suggest ordering a 4D3, or 4D8 for example if an OEM application calls for a 4D5 which is not available, instead of a 4E?

The numbers following the "-" denote the Major OD and is read as follows. "-60" is equal to 2.60mm OD.

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.

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The owners manual will show the needle jet in a carb diagram and yes, it does screw in or out. The needle fits into it. I use a S-7 on my '01 and it really improved the bike along with the Moto Tassinari reed cage. But since yours is an 02 it may be time for crank seals if they are original.

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Control the midrange circuit on Mikuni carbs by changing the nozzle (needle jet).     Changing the needle only make slight changes for very fine tuning.        Unlike Keihins where the whole  circuit is controlled by the needle only and changing the needle position will make a big difference,   Mikunis have an advantage for adjustment.

 

Edited by Greg Kendrick
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10 hours ago, Greg Kendrick said:

Control the midrange circuit on Mikuni carbs by changing the nozzle (needle jet).     Changing the needle only make slight changes for very fine tuning.        Unlike Keihins where the whole  circuit is controlled by the needle only and changing the needle position will make a big difference,   Mikunis have an advantage for adjustment.

 

This is a great piece of info, I knew you guys would have the answers! I went ahead and ordered an S8 (part # 784-13005-S-8) and S7 (784-13005-S-7) nozzle for experimentation. I used google earth to find the elevations of the trails I typically ride (1,300 feet), it's a useful tool!

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