Hey all,

When i first start my Z400, ever since having it rejetted after installing the upgrades listed in my Sig., Untill it warms up, if i rev it real quick, when i first hit the throttle, it sounds like the engine knocks. After it warms up, it runs great, but untill it warms up, its kind of rough.

Is this a lean condition? The overheat light has never come on, so i assume its not getting too hot.

When it was bone stock, it use to run very smooth, when cold, and when warm, now it just seams to be a bit rough.

P.S. What's the easiest way to get the spark plug out to check its color?

Thanks,

-TheChad

 

You didnt mention the jetting changes you made. The poping in the intake when cold, is a sign of lean mixtures.
Do you have a pilot jet, one up from stock? Hows the mixture screw set? Did you go for the highest idle, and then a tad richer from there? If this setting is about 4 turns out from seated, then you should put in the next larger pilot jet.

 

There is a crude spark plug wrench in your tool kit that came with the bike. Blow out the hole where the spark plug is with some compressed air to get the dust out, stick the wrench down the hole and unscrew the thing. A plug check may not show anything though, if it is only lean on the bottom end or when cold.

While you are at it, replace the plug with an Irridium one NGK# CR7EIX.

 

OK, I'll bite... What's the advantage of the irridium plug?

 

With irridium, I get a little better throtle response, particularly right off the bottom. The electrode is very hard, so it doesn't erode as fast, so it can be left in longer. That offsets the higher price. I get mine at http://www.sparkplugs.com/default.asp

See NGK's site for some more info http://www.ngksparkplugs.com/

 

I took the ATV in to have it rejetted, the guy that did the work said he rejetted it to DynoJet's Stage 2 w/ High-flow Intake & echaust Settings:

DynoJet Needle Groove #3
DJ150 Jet
Mixture Screw 3.5 Turns out

Thats all i know..

-ThaChad

 

The thing about those settings that come with the jet kit is, they just get you in the ballpark. You have to go out and ride it, then do the fine tuning.

 

What fine tuning? The mixture adjustment?

I'm true novice when it comes to tuning an ATV engine..

Thanks,

-TheChad

 

Try 1/2 turn out on the mixture screw, if this doesnt take care of the problem, then youll need the next size up, on the pilot jet.
Things like temperture, and altitude, and humidity effect the fuel mixture...it isnt usually a set and forget kind of thing.

 

The Mixture screw is the black **** at the back of the Carb (Looking from the Clutch Side) right?

Turning to the Right - Leaner?
Turning to the Left - Richer?

Thanks,

-ThaChad