To jet, or not to jet? 03' KX 125

[Porstala F9]

Hey guys. Ive had my KX 125 for about a month now. I am absolutely loving it. The only problem I have been having is the fouling of spark plugs frequently.

I have probably around 3 hours of riding time on the bike and have been through about 6 or 7 plugs. I have been running BR8ES plugs which I fouled a few of them + 1 stock plug + 1 BR8EG so far which I am using now.

I have thought that some of my previous plug fouling was my carelessness of revving the engine for about a minute to show it off to my friends, and one time riding without enough gas, and might have even been because I didnt warm it up enough before riding.

But I have never fouled a plug while riding for more than 5 minutes. The only times I fouled plugs was when I took the bike out after a previous day of riding once without stopping the bike at all. It seems that when I stop the bike after putting in a fresh plug, the next time when I go to start it up, it fouls within 30 seconds of when I take off out of nueutral. Maybe Im really not warming it up enough if this is whats happening? It has been pretty cold around here. The cold weather and snow here has also stopped me from doing much experimenting.

I went riding last weekend for about 40 minutes with a fresh tank of gas, fresh BR8EG spark plug and it was around 30 degrees Farenheit. I warmed it up for a good 6-8 minutes, or what seemd like a pretty long time. Was that long enough? I took off and rode for a good 40 minutes or so which was great (if it didnt foul while i was riding it this time, does this indicate i was riding it properly?) - I only started and stopped the bike that one time. I never started it since (its been snowing) - So what I did is I just pulled the plug out of the bike and took some pics of it. The outer ring(?) of the plug is a shiny silver, but the electrode thing is black and the inner circle thing is pretty blackish brownish.

http://hometown.aol.com/blinkoneatey2/index.html

I posted some pics of the BR8EG spark plug after about 40 minutes of riding there.

Should I consider jetting or wait until I break the bike in more, or does anyone have any further advice for me with this bike and these issues?

Thank you in advance! I appriciate any replys!! :)

 

[marcusgunby]

Its a jetting problem, on mine i ran a 35 pilot, Air screw 1.5, needle in the middle clip and a 400 main jet.

 

[holeshot]

Originally posted by marcusgunby
Its a jetting problem,

Tru Dat

The '03 KX125's arrive jetted too rich. You might want to move the needle clip to the second position from the top (third from the top is the middle position, which is stock). Gradually move leaner on the pilot jet (stock is #40 -- #37.5, 35 and 30 are available) until the spooge cleans up.

I've had to go all the way to #30, and it still runs a bit rich at 2500 ft (it's pretty close at 800 ft elevations though). Mine runs a bit richer than most, so don't go by my settings. Experiment.

 

[MXP1MP]

I would suggest going to the plug the '04 runs, the NGK R-16918B-9 main change was cause the stock b9EIX's electrodes were breaking off and for $25 for a plug that resists fouling better and won't break vs a new top end is worth it. It doesn't run BR9EG's stock, that might be part of the problem also. But so far I have leaned out the pilot to a 35 clip in the middle and one lower on the main to a 410 on my '04 and it runs great now.

 

[Porstala F9]

Thanks for the replies guys :) I appriciate those and any other comments anyone has!

Originally posted by MXP1MP
I would suggest going to the plug the '04 runs, the NGK R-16918B-9 main change was cause the stock b9EIX's electrodes were breaking off and for $25 for a plug that resists fouling better and won't break vs a new top end is worth it. It doesn't run BR9EG's stock, that might be part of the problem also. But so far I have leaned out the pilot to a 35 clip in the middle and one lower on the main to a 410 on my '04 and it runs great now.

Yeah, Ive been advised to switch to the 04 kx125 plug as well. However, I didn't do that yet since I wanted to experiment with fouling the cheaper plugs instead of a more expensive one. 3$ vrs 25$ - I'm running a BR8EG and it seemed to run fine. I also ran BR8ES's as well. Are these the wrong plugs, and maybe why they have fouled up so quickly? The BR8ESs were reccomended by the dealer, and the BR8EG's were reccomended by a friend.

I personally don't know a THING about carbs. But my father who was an big car guy back in his day assures me he knows quite a bit about cars (for example the old corvettes when they hard carbs) So do you think he would be able to help to tune the carb with me if he is familiar with carbs in general, but not 2-stroke carbs?

And again, thanks for the replies and suggestions guys, I really appriciate it.

Also, one more really quick question I have.. When Im riding the bike, the suspension is very good, however the front forks seem very stiff. Maybe its because I am a pretty light rider at only 115 pounds or so? I was told to put a higher viscosity fork oil in, ie: 10W instead of the stock 5W, since these bikes are designed for much heavier riders? Is this true? Or is it that I really probably just havent broken in the suspension with only about 3 hours, of rarely jumping the bike? (never been to a track yet)

k, thanks again!

 

[MXP1MP]

I know that my lil bro's 96 RM 125 it runs the same plug in it now as my 04 just it's an #8 not a #9 I have found the #8 plugs the suzuki's take are cheaper and much easier to get right now. My local dealer had to special order the plug for me directly threw kawi. But back to why I think the BR9es's are fouling out fast is cause that's what the guy my lil bro bought the bike from was running and it fouled them out pretty fast maybe 30 mins of ridding didn't matter if you was lugging it or screaming. Soon as we swapped to the more expensive special ngk racing plug it hasn't fouled since and the plug is like 5 months old. I have about 15 hrs on my stock 04 plug and it hasn't fouled at all or even shown signs of fouling.

As far as changing the jetting it's actually quite easy, run the jet spec's listed above those sound like they would work really good. It's basically what i'm running now I'm actually thinking of going to a smaller main from the 410 to the 400 i'm still getting alittle bit of oil out of the silencer. But my electrode is burning the nice tan color you want to be.

As for the fork, going to 10 wt oil would actually only make it stiffer, I don't have any real problems with the fork on my '04 but i'm 140 lbs so it's valved closer to my wieght. But whenever I'm trail ridding it and it repetetive bumps like roots/rocks it does seem to like get a pumping sensation and it feels really stiff in the first few inchs of travel. But the forks on my '04 or the bladder forks and your bike has the rubber bumper forks more like YZ's. I only notice it at slow speeds though. I think it's more design/valving related more than anything. It's a minor gripe for me cause I mainly MX and on the track it's excellent. Does your clutch make a slight whinning noise in the very initial part of engagement? Mine does, but all it is, is a noise you guys think it's cause the clutch has those rubber cushions?

 

[marcusgunby]

I would use a 2.5 wt oil in the forks -never a 10wt.

 

[va_yzrider]

I would spend that $25 on Eric Gorr's book instead of that plug to learn how to jet your bike properly (but that is just me). It really is a simple trial and error project. Once you get your jetting set correctly you will wonder why you didn't spend the time to do it sooner. A plug (I run NGK BR8EG) will last a very long time under the correct jetting conditions. The only time I change plugs is when I start feeling guilty for not doing it.

 

[va_yzrider]

Oh yeah, I get the NGK BR8EG plugs for about $2.50 at the local Napa store.

 

[Porstala F9]

Yeah, I was thinking about picking up that book. I have heard very good things about him. I read his website constantly to try and get a better knowledge about these motors, but its hard stuff.

Thanks for the replys guys!