Jetting...I can't believe the difference

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#1
After riding around since February with my needle jet in the top position as a free way to lean out my '98, I finally decided to take the advice our veteran posters and re-jet my baby. I ordered a 155 main and 45 pilot from Rage Performance and installed them this evening in 20 minutes. I can't believe the difference. This bike absolutely screams on every level. What's more, I really didn't think be able to tell the difference. I am now a believer in this and HIGHLY recommend it to anyone riding a KDX. Thanks to all the posters on this topic. BTW...it's only $20 and 20 minutes 20/20.
 

KDXFreestyle

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#2
my bike came jetted rich stock. i drilled out 3 1 1/4 hole sin my airbox cover, and removed the snorkel. it was still alittle rich. I added the FMF Powercore 2 silencer, now my jetting is spot on. tan plug
 
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#5
(I have no idea why I bother...)

re: '..jetting is spot on. tan plug'

To be frank and to the point....those two items have nothing to do with each other. The fact that your plug is 'tan' might be nice when taken as a fashion statement (Oooohh...I like the tan with the kawi green combo!). As far as it showing anything about jetting......it doesn't.

knoxkdx...but wait.......there's more!! ;)
 

KDXFreestyle

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#6
on motocross.com , it says if your running a tan plug, your jetting is correct. Black spoogy plug means to rich, and like white, or carbon means to lean. Just thought Id let ya know.
 

jboomer

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#7
As far as it showing anything about jetting......it doesn't.
That's a bold statement Canyncarvr!

That being a blanket statement....you're wrong. If he's performing the correct technique for a plug chop, then I'd say he's pretty close.
 

Braahp

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#8
He is right..................plug color is useless anymore with todays fuels. Thats just the only thing anybody ever hears as to how to check. I've seen it preached on here thousands of times. Sure it will get you in the ballpark but thats about it. Most people don't even know where to look at the plug.
 

jboomer

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#9
The ONLY other technique I've seen posted is the "Feel" method. Are you saying that is the most reliable technique? Hardly. You couldn't possibly be referring to jetting for spooge and smoke. The only other alternative is to jet using the plug chop. If one were to run a search on the subject he would immediately have access to a wealth of knowledge on the technique and where to look if searching for optimum results---I think it would get you way closer than a ballpark setting. If you've got a tried and true, BETTER technique, then by all means, spare us the suspense!
 

Braahp

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#10
Yep....the ol' "feel" method for throttle response and transitions. Thats what your jetting for anyways isn't it? You can tell if its rich or lean just by how it runs. For the main jet plug chops just aren't that reliable unless you can run at full throttle/ full load for 4-5 minutes to get a good coloring. Almost impossible to do that on a dirtbike. Plug chops are the most basic for most to do and thats all that has been shoved at you. Hey I still look at plug coloring too but don't rely on it totally. I use a PET digital tach on mine. At WOT RPMs will drop if you are lean.....drastically if you are real lean.....they won't reach peak RPM if you are rich......they will stabilize if you've got it right on. There again.....you can feel if its running rich or lean. Common sense tells you if its smokin' or spoogin' you know its over rich. Do you really think the top tuners rely on plug chops?.....Not.
 

Rich Rohrich

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#11
Originally posted by Braahp
For the main jet plug chops just aren't that reliable unless you can run at full throttle/ full load for 4-5 minutes to get a good coloring.

4 to 5 mintues at WOT? :scream:

You can get a totally reliable and dead on accurate plug chop on a fresh plug from a nine second dragstrip pass. The same can be done in a similar time frame on a dirtbike running up a short hill or moderate incline that puts consistent WOT load on the engine. Longer time frames at the same load will tend to make reading easier. Unleaded fuels will still produce a good plug chop if you are looking in the right place on the plug. Looking in the right place is the KEY, and probably the area where there is the most confusion.

I don't know anyone other than the guys at Bonneville who can run WOT for 4-5 minutes. I'm not sure if there is a KDX class out there though. :laugh:
 

Jaybird

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#12
http://www.strappe.com/plugs.html

The guy who wrote this ^ may have known a thing or two about it.
Perhaps one day we will venture into stator adjustments. (shrug)

Naaaa...arguing about plug colors is much more fun. It has to be fun, it gets done weekly it seems.
 

canyncarvr

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#13
That's a bold statement Canyncarvr!

That being a blanket statement....you're wrong.
Thanks for straightening me out! I appreciate your showing me the error of your ways.

..wait.....is that right? ;)

Only weekly? You need to check in more often!
 

Jaybird

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#14
On the defense of those who look at the pretty tan plug color...I should have said: "Gets done weakly" :)
 
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#15
Plug color is good for one thing: heat range. The tan color will tell you that your plug is the proper heat range for your conditions. Otherwise look at the ring at the base of the insulater. Cut off the threads of the plug to see it well. The thickness of this ring will tell you the correctness of your jetting. A 1mm ring is considered safe. Less and you might find problems with altitude changes, air density, ambient temperatures. Warm up your bike with a used plug, change to a fresh plug and run the bike under load for 20 seconds more or less. A hill provides good load but if a hill isn't available, then drag the rear brake. There's more on CD's site on how to perform the chop portion.
If I am incorrect on anything, let me know. This is how I understand to do it anyway.