Carb Guys/ question on Keihin jet needles

[Jay]

I have a listing on jet needles from a polaris performance seminar manual, they are listed in this order.
R-1370G
R-1368G
R-1371J
R-1370J
R-1369G
R-1372J
Question is are these listed in order from rich to lean/lean to rich or just random order? Which needle is richer a 1370G or a 1370J? I'm putting together an ET770 based on a '98 700 rmk and will be using Keihin carbs at first ( I have a set of 40mm rack mikunis bored to 41.5 coming ) so if anyone has any advice for specs on either setup I'd sure appreciate it.

P.S. happy new year
Jay

 

[xcmark]

If the tm 40 carbs are due in shortly dont spend any time of effort with the old school carbs.

straight diameter section: in keihin carbs either the last two digit or the last letter denote the diameter of the needle. The higher the last two numbers the leaner the needle the lower the letter the richer the needle. By going to a thinner needle there is a larger area between the jet needle and needle jet supplying a richer mixture.

 

[Jay]

Thanks xcmark, anyone else got any setups?

 

[Jay]

ttt

 

[snoboy]

13 = taper of needle

 

[snoboy]

*13 = taper of needle (I think 14 is fatter taper than 13)
*68,69,70,72 etc. = diameter 72 is larger diameter and therefore leaner ie.
it plugs the hole more letting less fuel pass through.
*G, J = height/length of straight portion of needle between where E clip notches are located and taper begins .

I don't remember which is richer between G and J but I can tell you you wont get much change on the letter as you would changing E clip positions. I f--ked around with Kehin needles for 7 friggin years (I have about 8 different sets of needles) and finally switched to Mikuni 40 flatslides and it felt like I added a pipe to my sled. I haven't had to touch my carbs since.

These are Polaris numbers. Kehin numbers are 3 letters designators like CEN, CCN, CCM etc. Good luck with the Kehins. BTW I've got needles for sale he he.

snoboy

 

[Backcountry]

The R series Keihin needles are typically the OEM type part numbers.

Here's some links to info:
http://www.dirtrider.net/justkdx/jetneedles.html
Dont get scared that they talk alot about KDX bikes, Keihin needles are Keihin needles. You may find that the L1 number doesnt convert- its a proprietary L1 for the manufacturer. You can measure it and compare.

http://www.motorcyclecarbs.com/keihin__jet_needle_W52.cfm
More jet needle conversion information.

You can also go to Sudco.com then products, then keihin jet needles

Keihin carbs work just as well as Mikunis. Its a matter of preference. I prefer Keihins over Mikunis- I feel Keihins are easier to tune, easier to decode what the heck a needle means with 3 letters instead of 7 letters and numbers, and pilot jet changes dont influence the whole circuit. What I typically find is that they are not as sensitive to what needle part number they have in them, but more so to what size pilot you are using. If it still muddy in the middle then a clip position change can work. Only rarely do I jump from a C series to a D series needle. I would start with the 1368G but Ive also had good luck with CEL needles in alot of stuff. DGK's have also worked well but they are a bit richer...

Remeber hard fast bog = lean
Slow and dull to build RPM = rich
Always always start rich and work your way down!

 

[Jay]

Thanks for the info guys.