YZ426 Jetting Boosts YZ400 Midrange Power

8 replies to this topic
  • James_Dean

Posted February 10, 2001 - 08:52 PM


Have any YZ400 owners been using a YZ426 carb needle for increased mid-range power?

This gives more pull at 1/2 throttle by increasing fuel delivered through the primary fuel circuit. A smaller main jet is to be expected, #162-#172 (??)

If you are running an EKR, EKP, or EKN in a YZ400; What pilot and main jet are you running?

The graph below shows the impact of the needle taper on fuel mixture. The stock '01YZ426 uses EJP#4 which is 1/2 clip richer than an EKP#4.

If you're interested, the part numbers are:
#EKR - 5JG-14916-ER (leanest 0-1/8)
#EKQ - 5JG-14916-E1
#EKP - 5JG-14916-EP
#EKN - 5JG-14916-EN (richest 0-1/8)


James Dean :)
Posted Image

[This message has been edited by James Dean (edited 02-12-2001).]

  • Ken

Posted February 11, 2001 - 03:22 PM



Ordered an EKP & EKN- still waiting… Dealer called and said one of the two arrived but the other backordered until mid March.

Maybe a while before riding anyway as winter finally got here with snow. I'll let you know what I sort out on my '98 YZ.


  • Shawbridge Husky

Posted February 12, 2001 - 01:50 PM


Nice of you top share James Dean! I am presently rebuilding my '99 and have added WB header pipe and E-series spark arrestor as well as 420 kit. Would your suggested jetting work on the east coast at 0-3000'?

  • James_Dean

Posted February 12, 2001 - 07:51 PM


Yes this will work for your east coast conditions too. I would suggest you ride the 420 first with stock jetting and then with an EKP#3 or #4 to see a direct comparison of what the needle does. The gain in response is at 1/2 throttle. Uphills and out of corners the bike takes less throttle to pull forward.

I didn't like the feel of my stock 400 mid-throttle jetting on uphills, expecting more, then bought varied needles to come up with this. The needle to use was obvious. The '01YZ needle is slightly richer than what I was running last summer in my '00WR400 with YZ exhaust(by 1/2 clip).

The EKP was recommended to the guys on the WR forum last summer, but it's hard to convince anyone of the difference it makes until they ride it. Especially when their bikes are already running good. The power delivery feels more like a 2-stroke when trying to lift the front end.

I get nothing more from this than the satisfaction that people get to feel the power of jetting. :)

James Dean

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  • Guest_Guest_*

Posted February 15, 2001 - 01:59 PM


James Dean,
I went to the dealer today to try and get the EKP needle for my 400. The dealer could not find that needle. He said the don't make that one. What needle should i use for my yz400.

  • Hick

Posted February 15, 2001 - 04:55 PM


Not again…

Spud, his problem is likely due to the needle being mislabeled on the Yamaha parts catalog or fiche. Go back in and say, “Sorry, I’ve changed my mind, I would like an EVP instead of the EKP!” and you will get an EKP, the letters, as you probably know, are stamped right on the needle.

Fiche says EVP, EVQ, EVR, but order the associated PN and you will get EKP, EKQ, EKQ.

Better yet, here is the PN for an OBEKP needle: 5JG-14916-EP

Hope this helps!

  • James_Dean

Posted February 15, 2001 - 06:48 PM


Hick is right, but be sure and use the YZ426 parts option.

As I said before, the parts department has it wrong. Go to the service department and look it up in the '00YZ426 service manual.

You MUST order the number 5JG-14916-EP exactly as Hick said. DO NOT ORDER 5BE-14916-EP.

(Hick, that suggestion about asking for an EVP would have ended up wrong if they looked in the YZ400 parts option.)


  • Guest_Guest_*

Posted February 15, 2001 - 11:10 PM


Thanks guys. I will give it a try tom. Sorry about my brain failure. I should of paid more attention to the first post.


  • Shawbridge Husky

Posted February 16, 2001 - 02:23 PM


Thanks for sharing the info guys! Will order the part tomorrow monrning.

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