Need help with my Z400

[littlebus]

I got a 03 LTZ 400 and recently I put a k&n filter on it and it ran like sh*t after I installed it. I talked to a few people and they told me I need a jet kit. I got a jet kit and put in a 150 main jet. Now the bike runs like complete sh*t. Before I did the jet kit I could ride it but when I floored it it would break up in high rpm's. Now it is unrideable. For my mods and elevation I am pretty sure I have the right jet in there. I have a yoshimira slip on, Homemade K&N filter, cut up air box with no lid. If I posted this in the wrong section im sorry but didnt know where else to put it. Thanks for any help you guys can give.

[Ida_Mann]

This would be the wrong section but let's leave it here for a little while so many ccan see it first.

I'm sure someone will come along with a good suggestion soon.

I unfortunately don't have one unless your 400 has a computer in a saddlebag on the side ;-)

Id@

[SomBch]

just of the top of my head , sounds like your suckn to much air and not enough fuel.try the next bigger and see what happens, With the mods you described thats probably the case.

[littlebus]

Ok I just got done messin with it for the first time in a few days and I took it for a ride. It idles like sh*t at first but then I kept reving it up till it sounded like it cleared out and i dumped the clutch and off we went. This thing was like a whole diff machine but then when i slowed down to turn it ran like sh*t and had no power at low rpm's. As soon as I took off and got up in the rpm's it was like a raped ape again. Maybe it is flooding itself? Should I change the a/f screw adjustment. I got it at 3.5 turns now.I just need some low end on this thing now and ill be golden.

[SomBch]

does it sound like its running out of gas or is it bogging like its flooded

[littlebus]

It was breaking up and poping out of the intake. I am an ase certified mechanic and I couldnt even tell if it was rich or lean. I think it is rich but im not sure. If I move my pin down a notch what will that do?

[kfx400rob]

you need to adjust the air fuel screw and u need to put a 160 main jet in, and that should make it run fine

kawasaki400racer

[SomBch]

yea, what he said

[klutchbuster400]

Sounds exactly what happened to mines, Look up my screen name in the teh corner to se what some people posted.
We tried  2 different carbs, stock and aftermarket and niether worked. We tried a stock cdi box and that didnt work.
Surprisingly an aftermarket cdi box and top end sprocket it fixed it. Well I cant say fixed, It stalled the sputtering alot, then I switched mack to my old sprocket, and the problem seemed to go away by itself. BTW, this happened when we put in a jet kit.

[littlebus]

A 160 is richer right? If it is falling on its face at low rpm's wouldnt that indicate that it is to rich or are 4 wheelers diff? What should i adjust the a/f screw to? Thanks for all the help guys.

[Mars]

Littlebus,
 Back up a few steps.
1. Your air filter and intake must have a good seal. Go there first.

2.Make sure your "choke" plunger has a good seal.(o-rings)

3.Pull your spark plug see what it looks like.

4.You need a 150~165 main for a Yoshi. But you must know who made the jet you installed. Some brands use hole size and some use flow rate for sizing. Your air screw only affects idle.
I have yet to see a stock bore/cam/carb 400 need a larger low speed jet.
 It is possible you got some trash in the idle/low speed carb circiuts when you replaced the main hance the poor idle/low speed performance.

PS. ASE double master and EVT cert. I still get stumped once in a while.
 

[blindkaeta]

165 main
45 pilot
air screw 2.5 turns from tight
needle in pos #3 which is middle
if that doesn't work your problem is not in the jetting.

[littlebus]

Littlebus,
 Back up a few steps.
1. Your air filter and intake must have a good seal. Go there first.

2.Make sure your "choke" plunger has a good seal.(o-rings)

3.Pull your spark plug see what it looks like.

4.You need a 150~165 main for a Yoshi. But you must know who made the jet you installed. Some brands use hole size and some use flow rate for sizing. Your air screw only affects idle.
I have yet to see a stock bore/cam/carb 400 need a larger low speed jet.
 It is possible you got some trash in the idle/low speed carb circiuts when you replaced the main hance the poor idle/low speed performance.

PS. ASE double master and EVT cert. I still get stumped once in a while.
 

I am running a dyno jet kit, I cleaned the carb out very well when I had it off the bike so im sure there is no crap in it, a/f is on tight, and choke o-rings are good.

[Muddbuggy]

I put a jet kit and pipe and filter on mine too and cleaned the carb while I had it out and about 15mins. in to my first run the bike fell on its face everybody said check this check that, never did I think of a piece of trash in the jet b/c I was just in the carb but a small piece of trash must of got by my fuel filter and wedge itself in my main jet and then the problem was solved.  I put the full yoshi exhaust on my quad and I had to step up to the next size pilot from stock and Im running a 165 main too.  Also I am running a K&N fliter lid only and my A/b is sealed.

MB

[klutchbuster400]

Littlebus,
 Back up a few steps.
1. Your air filter and intake must have a good seal. Go there first.

2.Make sure your "choke" plunger has a good seal.(o-rings)

3.Pull your spark plug see what it looks like.

4.You need a 150~165 main for a Yoshi. But you must know who made the jet you installed. Some brands use hole size and some use flow rate for sizing. Your air screw only affects idle.
I have yet to see a stock bore/cam/carb 400 need a larger low speed jet.
 It is possible you got some trash in the idle/low speed carb circiuts when you replaced the main hance the poor idle/low speed performance.

PS. ASE double master and EVT cert. I still get stumped once in a while.
 

When we jetted my bike, it wouldnt allow a 150 jet, ran like crap, we have to run a 142

[MuddFreak77]

Don't forget when you re-jet you need to adjust the air/fuel screw too.  If you don't it will run like SHAT. 

[littlebus]

If I am getting a little to much fuel at an idle but not at wot how would I fix that? a/f screw is 3.5 turns.

[Chuck_Norris]

[ a/f is on tight, and choke o-rings are good.

Great information Mars!!!

Littlebus: Are you saying the the air flow screw is turned in all the way tight? if so then you adjust it outat least 1.5 turns depending on how the bike runs. ensure that each jetting change you make you are using a clean spark plug. Something you might consider it the Jet4Power system. I have a link of the system in the tech section. scope it out, I run it on my YFZ 

[littlebus]

[ a/f is on tight, and choke o-rings are good.

Great information Mars!!!

Littlebus: Are you saying the the air flow screw is turned in all the way tight? if so then you adjust it outat least 1.5 turns depending on how the bike runs. ensure that each jetting change you make you are using a clean spark plug. Something you might consider it the Jet4Power system. I have a link of the system in the tech section. scope it out, I run it on my YFZ 

When I say a/f is tight it means Air Filter. Air fuel screw is 3.5 turns.

[klutchbuster400]

sounds familiar.

check this post out. alot of good advice.

http://www.atvflorida.com/forum/index.php/topic,11897.0.html

also the main jet doesnt affect af mixture at idle. that jet works at mid and full throttle.
lowering the clip(raising the needle) will richen it and the opposite will make it go leaner. the needle usually effects mid throttle and may give you a  flat spot.

also you can find alot of useful info here:
http://www.z400central.com/invision/index.php?act=Search&CODE=show&searchid=cfe0d28afd038abf7e9daa1b87847cf5&search_in=posts&result_type=topics&highlite=dynojet


HTH, gery350

[gery350]

also check this out:

old school sent me this to help me out and it was great.
it explains everyhting about how the carb works..jets , needle, etc.

http://www.motocross.com/motoprof/moto/mcycle/carb101/carb101.html

[Mars]

http://www.motocross.com/motoprof/moto/mcycle/carb101/carb101.html

Great link Grey.

Jetting is one of those things that make you go hummm.
eg: Son-inlaws bike 03 Z400, jet kit 155 main, middle needle clip, air screw about 3 out.
My 04 Z400 165 main,done.
Both have Yoshi Tri-ovals, both run perfect.

[bluesman]

check the tank vent??

[littlebus]

Ok thans for all the help. I started with the easy stuff first. I mover the needle down a notch and a/f screw in a half turn and it got worse. I moved the needle up 2 notches and the a/f screw to 4.0 turns and it runs like a champ now.