Jetting of a kx125.

[syko]

I yet again need some help for jetting my kx125 2004 model.
it's broken in and been stripped down and had all done that needs to be done after break in.
the bike is running rich, as expected.
so i've taken off the carb ready to lean it out a little.
i took it too my local practice track the weekend, it's a very bumpy, jumpy track and there are few places to really let rip and open up the throttle, so i was mainly in 1st gear and in sections second gear but never above second at any point. when it was in 1st gear it was ridden right at the top of it's gear for the most part.
i fouled 3 plugs that day so it is obviously rich. the weather at the moment is just warm. not hot at all but warm enough to get away with a t-shirt, although it has been pretty windy. no idea what altitude is here in the Uk. (sorry if my weather report is a bit vague)

so anyways, i took off my carb ready to lean it out.
the stock settings are:
jet needle- 6CHJ10-82
jet needle clip position-3
pilot jet-40
main jet-420
air screw opening-2 and a half.
i've been running a fully synthetic race oil at 32-1 and i've been running BR9EIX plug.

what do you guys think I should be changing my set up too?

in my spares kit i have
pilot jets: 37.5/ 42.5
main jet: 410/430
jet needle: 6CHJ11-82


also, with the pilot jet and main jet what exactly equals 1 size up or down. e.g would one size up on a main jet that is 420 be a 421 or does it go up in 10's? and if my pilot jet is 40 is 1 size up a 41 or does that go up in .5's?
hope that makes sense!


thanks once again in advance.

 

[Porstala F9]

I yet again need some help for jetting my kx125 2004 model.
it's broken in and been stripped down and had all done that needs to be done after break in.
the bike is running rich, as expected.
so i've taken off the carb ready to lean it out a little.
i took it too my local practice track the weekend, it's a very bumpy, jumpy track and there are few places to really let rip and open up the throttle, so i was mainly in 1st gear and in sections second gear but never above second at any point. when it was in 1st gear it was ridden right at the top of it's gear for the most part.
i fouled 3 plugs that day so it is obviously rich. the weather at the moment is just warm. not hot at all but warm enough to get away with a t-shirt, although it has been pretty windy. no idea what altitude is here in the Uk. (sorry if my weather report is a bit vague)

so anyways, i took off my carb ready to lean it out.
the stock settings are:
jet needle- 6CHJ10-82
jet needle clip position-3
pilot jet-40
main jet-420
air screw opening-2 and a half.
i've been running a fully synthetic race oil at 32-1 and i've been running BR9EIX plug.

what do you guys think I should be changing my set up too?

in my spares kit i have
pilot jets: 37.5/ 42.5
main jet: 410/430
jet needle: 6CHJ11-82


also, with the pilot jet and main jet what exactly equals 1 size up or down. e.g would one size up on a main jet that is 420 be a 421 or does it go up in 10's? and if my pilot jet is 40 is 1 size up a 41 or does that go up in .5's?
hope that makes sense!


thanks once again in advance.

dont change the jet needle, just change the clip position on it up one. this is something mostly everyone does with their bikes to lean the jetting since its one of the biggest factors in jetting and is responsible for the majority of the throttle range.

i ran it in the second clip positon from the top counting down, which is just up one from stock, and put in a 37.5 at first and it worked pretty good and i wasnt fouling as many plugs. i have a 35 in there now because it is supposed to be wamer out around here and hopefully if its 80° like they say it will be, i may have to put a 32.5 in. so try 37.5 and work backwards until it gets good. and dont put the air screw too far out if you dont have to, since its a better thing to just get a leaner pilot. also, i ran a 410 main and only 1.5 turns on the air screw.

also, the eix plugs suck dude. once u get the jetting right, switch to the plugs that the rm's use, but for now, even an br es plug would be good to experiment with. the eix plug ruined this dude on heres top end.

 

[syko]

cheers man.
much appreciated!
i'll give it a go.

 

[Porstala F9]

I yet again need some help for jetting my kx125 2004 model.
it's broken in and been stripped down and had all done that needs to be done after break in.
the bike is running rich, as expected.
so i've taken off the carb ready to lean it out a little.
i took it too my local practice track the weekend, it's a very bumpy, jumpy track and there are few places to really let rip and open up the throttle, so i was mainly in 1st gear and in sections second gear but never above second at any point. when it was in 1st gear it was ridden right at the top of it's gear for the most part.
i fouled 3 plugs that day so it is obviously rich. the weather at the moment is just warm. not hot at all but warm enough to get away with a t-shirt, although it has been pretty windy. no idea what altitude is here in the Uk. (sorry if my weather report is a bit vague)

so anyways, i took off my carb ready to lean it out.
the stock settings are:
jet needle- 6CHJ10-82
jet needle clip position-3
pilot jet-40
main jet-420
air screw opening-2 and a half.
i've been running a fully synthetic race oil at 32-1 and i've been running BR9EIX plug.

what do you guys think I should be changing my set up too?

in my spares kit i have
pilot jets: 37.5/ 42.5
main jet: 410/430
jet needle: 6CHJ11-82


also, with the pilot jet and main jet what exactly equals 1 size up or down. e.g would one size up on a main jet that is 420 be a 421 or does it go up in 10's? and if my pilot jet is 40 is 1 size up a 41 or does that go up in .5's?
hope that makes sense!


thanks once again in advance.

I think I may have told you this allready, but at first, all I did was put the air screw at 3 turns out and then put the needle up a clip and it did me wonders. Going from fouling plugs every ride, to over fifteen. I have got a 37.5 in there now and the thing has still yet to foul a plug since I took off the carb. I would try moving the clip up one position, and putting in the new pilot to start out and see how it works for you.

To your other question - The pilot sizes go in 2.5 step increments. So 45, 42.5, 40, 37.5, 35, 32.5, 30.. etc.. The main jet sizes go in 10 step increments. 440, 430, 420 410, 400, 390, 380, etc..

One more thing, I would reccomend trying 8 heat range plugs instead of the 9s. And as mentioned, the EIX plugs are pretty crappy. They are three times the price of the BR8EGs I run, and they do a great job. If you arent riding the hell out of the bike, a BR8 heat range would be a better option. They worked much better than the 9s for me, so its worth trying out :)

 

[syko]

I dunno what i'd do without you guys! you are awesome!

makes me proud to be part of the MX world knowing that guys like you are part of it too.


just so you know, i've knocked the jet needle up one clip, i put in a 37.5 and i've also changed the main jet to a 410.
i'm gonna mess around with the air screw once i get it all back together and get out on the thing.
i'll keep you posted on how it goes.
thanks again!

 

[UK KXER]

Syko how did these settins work for your bike ? as I to am in the UK and have a 2004 125 that needs a little jetting to get it bang on

Cheers UK KXER

 

[MXP1MP]

I ran in my '04 KX with stock plug (the exspensive one!) #35 pilot #2 clip pos from top #400 main air screw 1.5 turns out and it ran like a champ! Once I put in those spec's I didn't have mess with it again! I rode it for over a year about 70 hrs on the same plug. Low temps to high temps yea up in the mid 90's! low alitudes up to little over 4000 foot above sea level it ran the same always on those spec's. It never pinged and it never detonated didn't matter if it was pump 92 or race gas. My plug was always the TAN colored electrode on those spec's. Don't tell me it's to lean I used to rev the piss out of my KX alot. oh yea this is at 40:1 mix.

 

[SirHilton17]

I ran in my '04 KX with stock plug (the exspensive one!) #35 pilot #2 clip pos from top #400 main air screw 1.5 turns out and it ran like a champ! Once I put in those spec's I didn't have mess with it again! I rode it for over a year about 70 hrs on the same plug. Low temps to high temps yea up in the mid 90's! low alitudes up to little over 4000 foot above sea level it ran the same always on those spec's. It never pinged and it never detonated didn't matter if it was pump 92 or race gas. My plug was always the TAN colored electrode on those spec's. Don't tell me it's to lean I used to rev the piss out of my KX alot. oh yea this is at 40:1 mix.

I have the same specs... except for im on the 1st clip pos... and i run br9es, 32:1
i am going to change over to the 2nd clip pos cause mine will ping when you rev the piss out of it...

 

[UK KXER]

Thanks for your input lads I will give it a go today and will let you know how I get on

 

[UK KXER]

Just got in from garage I have put in have
410 main
37.5 pilot
grove 2 on neddle
2.5 turns out on the air scew
Now the bike has a slow tickover and the engine picks up nice from the bottom without a load on the engine

But once on the bike it picks up okish sort o hesitates a bit then takes off well
What do I need to adjust to get rid of the slight hesitation ?

Cheers

 

[MXP1MP]

err what does slow tick over mean? you mean it's idling slower? does hesitation mean bog and where in the throttle is this happening? I wish I still had my service manual it used to list the jetting spec's for all models u.s/euro. I recently sold the bike. I vaguely remember the euro model might of had a different needed like it was one richer?

 

[UK KXER]

err what does slow tick over mean? you mean it's idling slower? does hesitation mean bog and where in the throttle is this happening? I wish I still had my service manual it used to list the jetting spec's for all models u.s/euro. I recently sold the bike. I vaguely remember the euro model might of had a different needed like it was one richer?

Slow tickover does mean idle and yes it bogs a bit at 0- quarter throttle sorry about the Englih termenology

 

[MXP1MP]

Thats what I thought :) i got this from kawaski.com this is the needle that is spec'd stock in the U.S/Canadian models 6CHJ10-82 The alpha letter up front stay the same is the last 4 numbers that matter. 10 is stock clip pos if it's an 11 it is either a half clip leaner or richer position but thats not real important at the moment. the last number the 82 dictates if it's leaner or richer I'm not sure if 81 or 83 would be leaner I'm going to assume going down in numbers is leaner. example 6CHJ10-81 is leaner than 6CHJ10-82. but it could be the opposite also since it's more common to get 95 octane at the pump there.

I thought the euro model's had the 83?

 

[UK KXER]

Just to update things have been having a fiddle with the air scew and it is very nearly there. But as it has been snowing quite a bit not been able to do much road testing

 

[MXP1MP]

Thats kewl it was just the air screw it was my first assumption but I got over techincal in my diagnosis once again. :blah:

 

[NM_KDX200]

I ran in my '04 KX with stock plug (the exspensive one!) #35 pilot #2 clip pos from top #400 main air screw 1.5 turns out and it ran like a champ! ...alitudes up to little over 4000 foot above sea level

Sorry to dig up this old thread but I just bought an '05 KX125. I'm at 6,000-8,000'. It has a 410 and 37.5 and feels rich to me which makes sense since that's FMF's recommeded jetting for 3000' or less. I'm thinking on going to a 390-380 main and 35 or smaller pilot.

Anyone else run an '04-05 KX125 at my elevation?

 

[perfectdirtguy]

1.5 turns on the air screw

 

[MarKGftAV]

wow ive had my cr250 for almost 3 years now and am only on the 2nd spark plug