"S" pilot jets and HRC needles

What's the real deal with the "S" pilot jets (65s, 68s, etc)? I understand how they are physically different from standard Keihin jets (the "S" jets have smaller emulsification holes).

What I don't understand is why so many people seem to use and recommend using "S" jets (68s especially) versus the standard jets (like a regular 68). I am under the impression that the "S" jets are strictly a Honda thing that is related to emissions, NOT performance.

The reason I'm asking about this is because I'm using a 68 pilot jet with great results and I want to know why (if there is a reason) I should be using the 68s pilot jet so many others seem to be using.

Thanks.

ETA: I was gonna ask about the b53e needle but decided not to--yet my edited post title isn't showing up on the subforum list. :thumbsup:

There is no law that says you have to use it. The air holes are different as you said and so it affects the emulsification (mixture of fuel/air). The better they are mixed the better the mixture burns. I don't know that anybody ever proved that the "s" jets really worked better. If your bike runs good, that's all that matters. Though just for comparison sake, you might try the 68S and see if you can tell a difference in starting/throttle response etc...

What I don't understand is why so many people seem to use and recommend using "S" jets (68s especially) versus the standard jets (like a regular 68). I am under the impression that the "S" jets are strictly a Honda thing that is related to emissions, NOT performance.

NOT true. If anything, the "S" jets are the non-emission jets. The "S" jets have a different pattern of holes, and a slightly smaller size holes to help atomize the fuel into the air with a finer mist. The "S" jet richens up the bottom end just a touch. This will increase low-end responce, aswell as low end power & tourque.

68.jpg

68s.jpg

I think the HRC needle, by it's self, is a marginal difference. I have tried both needles, and there is a small difference. You are much better off with the 68s jet, versus the HRC needle. But for less than 20 bucks each, why not

I have tried every possible set-up on my stock carb, and using a 68s pilot & the HRC needle is by far the best performing combonation. They are a MUST have if you want to keep you with me. :thumbsup:

Hey like you I live at altitude, around 6k feet, I am going to try the stock slow jet but with a 168 main and see what happens, dealer did not have a 68S.

Wicked,

Dealers don't carry the 68s, usually they don't even have the part#. You can get the 68S, as well as all the other uncorking goodies, and many more from here;

http://www.angelfire.com/ut/moab/parts_frames.html

Go to the second drop down box and select "General XR Parts." This is where I got my 68s pilot and 13T front sprocket. The 13T is GREAT for tight/technical woods riding. This is the guy that used to run the Yahoo XR650R Group, so he knows a bit about the 650R. A good guy he is.

NOT true. If anything, the "S" jets are the non-emission jets...[snip]

If that is the case, then why are they the stock jet type and why are they a "non-standard" Keihin part that only Honda seems to use? I haven't seen any application of "S" jets other than on the 650R.

I'm not trying to be argumentative, I just want to understand. It seems more logical to me that the "S" jets are an emmisions device (albiet a minor one) used by Honda than the "S" jets being superior in anything other than emissions control. The very source of your pictures suggests that the "S" jets are in fact emissions related. http://xr650r.us/jetting/

If "S" jets are better, how come I've never encountered them until the 650R? Why don't all Keihins use "S" jets?

Has anyone done any dyno tuning to specifically uncover the precise performance difference between the two types?

Hey like you I live at altitude, around 6k feet, I am going to try the stock slow jet but with a 168 main and see what happens, dealer did not have a 68S.

Yes, we are at the same altitude. Here is my set-up. (my dealership had to order the 68s) You can go without the 68s, but you'll love the low-end power if you get one.

68s pilot jet (adjustment screw 2-1/4 turns out)

170 Main jet

HRC Needle set 4th posistion from top.

HRC intake manifold

HRC exhaust baffle (NOT the stock one drilled out)

K&N Air Filter

I have played with almost every possible combonation, and this is by far, the best settings for the stock carb. Around 9,000 ft., I have to turn my pilot adjustment in 1/4 of a turn. But other than that, this set up will run great from 5,000 ft to over 10,000 ft.

If that is the case, then why are they the stock jet type and why are they a "non-standard" Keihin part that only Honda seems to use? I haven't seen any application of "S" jets other than on the 650R.

First off, the "S" jets are NOT the stock jet. All stock XR650's (non-CA) came with a regular 65 pilot jet & a 125 main jet. As part of my "un-corking" the bike, I had to order the 68s pilot jet. I have a regular 68, a 70, and the 68s jets. The 68s makes the low-end power on the bike much better, simple as that.

I've heard the keihin & honda developed the "S" jets together for racing. They were made specifically for the XR650.

If you still don't believe me, cool, don't use the jets. All I know is, it was a huge improvement on my bike. Oh and BTY, The jetting guide on xr650r.us was WRONG for my bike. I set it up the way they said for my altitude & temp range, and the bike wouldn't even start. I had to find other research materials.

The stock pilot jet is a 65s on all XR650Rs. The only difference in the CA bikes is the smog pump. The jetting is the same.

The stock pilot jet is a 65s on all XR650Rs. The only difference in the CA bikes is the smog pump. The jetting is the same.

This is true!

68s pilot jet 99105-MBN-0680 ~ 70s pilot jet 99105-MBN-0700

70 (without the "S") is also a good jet for some.

Wicked,

Dealers don't carry the 68s, usually they don't even have the part#. You can get the 68S, as well as all the other uncorking goodies, and many more from here;

http://www.angelfire.com/ut/moab/parts_frames.html

Go to the second drop down box and select "General XR Parts." This is where I got my 68s pilot and 13T front sprocket. The 13T is GREAT for tight/technical woods riding. This is the guy that used to run the Yahoo XR650R Group, so he knows a bit about the 650R. A good guy he is.

I tried this website, but do not see the HRC needle for sale. Can you post the part#, and I will order it from my local Honda Dealer? I want to try it out, as I am running the stock needle right now. Thanks!!

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