carb tuning

has anyone out there tried experementing

with different jet needles on

98,99 yz400 ?

You need to buy James Dean's jetting a search on it! This spreadsheet is amazing! Thanks James Dean! Later,


that is a ridiculous thing to say!

the info is ten square on what needle and jetting this man wants. i've got that chart and as pretty as it is, it doesn't teach you how to be any good at jetting.

what happened to giving people free advice? i thought that that was what we wre here to do?


i know that if you give your altitude and area of riding there are still some here that will help.


Thanks Taffy.

I ride between 0 - 1000'

ambient temps around 40 - 50 f

the bike runs good,but i know it

can be better!

right now Im running

#50 pilot

#100 pilot air

#175 main


4th clip pos.


1.5 seconds duration

94 sunnoco pump gas

when i installed the p-38

the bike ran like **** .

i had a # 45 low

same needle 3rd clip, 175 high spd jet, i removed the carb and found that

after the p-38 i had no accelerator pump!

needless to say i wasnt happy.I tried several

times to contact factory r&d with no succsess

so i looked at it, and decided to grind the

tab on the diaphram 0.020". it worked!

but the motor felt soft through the mid.

so i richened the low spd jet to #50

and lowered the needle clip 1 spot

this improved it much from when i first

started but i know it can be better !

i think a different needle will do it.

but i dont know which 1 to get.

a bloke named james dean has recommended the EKP needle and i had the EMM and loved it.

i think for sea level the EKN would be excellent. your PJ @50 is very large and i think that you should start by getting your p-38 to work for just .5 seconds and then start from there.

i would try this

EKN clip 4

MJ down 10 to 165 this isn't me suggesting you lean off your jetting. the new narrower needle passes more fuel so you need a smaller MJ.

buy a Pilot Air Screw from sudco and turn it all the way in and then carefully out to 5/8th turn.

fit a 40/42 max PJ for sharper acceleration.

Ps to 1.5 turns.

your bike will need fettling from there but it'll be a lot quicker and if i can be of any help let me know.

you may want to go over to the WR side and read up a 200 reply thread named jetting Q's. it is now three weeks old so you'll have to get "view 30 days" up.

if you write everything across a sheet of paper as you go you can see how it evolves.

i've just helped "the missile" from switzerland and his bike is going very veryt well.

he's now changed to an open pipe as the snow fell. so we await a prper report but it looked like a drop of the needle was going to do the trick.



I have over a dozen needles in my toolbox that were tested in my WR400 with YZ exhaust/YZ timed and already given 3 needles away. Over 30 test runs were made with these.

Taffy has a good suggestion to use the EKN#4 (or EMN#5, ELN#4, EJN#3- all the nearly same). Use your best judgement on the pilot and main. The needle is richer in straight diameter and taper which calls for reduction at both ends (repeating what Taffy said). I would start with a #45/#170, before stepping down to Taffy's leaner setting.

The '01YZ's used EJP and ELP needles, EKP is between these in clip position. The spreadsheet decodes these and graphs the profiles with clip positions over each other.


The spreadsheet you have is only a fraction of what is in the new tuning guide. I will send you a complete copy. It took me the longest time to help others understand needle codes and their impact. I spent 3 months writing the new guide. This version explains needle codes in a matter of minutes with useful graphs. I know it will never be up to your standards. That would take a book. :)

You are right that this forum is about giving people free advice. I will not conceal anything because of the tuning program. Please let it stand for what it is, just useful information not available anywhere else, and others can pass their own judgement.


the rub on free advice was just a side swipe to calm people down. i've learnt a lot about the usa folk and everything seems to be like sweets in the shop window. it most certainly wasn't aimed at you.

when two people come at a problem from two different angles it's not always easy to keep it clean but we canna try ladie! (och i lannoo!).

my jobs pretty much done around here anyway and things are going to wind down as soon as i can break the habit and you can't beat a bit of hard graft for that to happen now can you!

o look! here comes another busy patch.


if you want any help on practical assesment and my thoughts to help you with your project then let me know. as you know though, i put EVERYTHING down.


Thank you both for your insight.

it sounds like both of you have spent

extensive time doing r&d.

and i greatly appreciate you

sharing it with me!

i'll let you know how it turns out.

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now