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KDX 250 still fouls plugs
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Posted by: GhostofSilverider---------------------

I changed the petcock that was leaking, but it still fouls plugs.
The jetting is stock on this steel tank euro model (main #152, not sure what the pilot is), despite a derestricted pipe which would normally call for a bigger mainjet. But I left it like I got it from previous owner (he did the pipe mod, added aftermarket silencer but left lid on airbox). That's because the bike appears already way too rich as it is (lots of spooge , outside and on the piston).
Previous owner was running a Champion N 2G, plug now replaced at Champion by RN2C, and that plug lasted a bit longer despite being colder than the B8ES I run (as recommended by manual). So now I am thinking switching to Champion RN3C (one step hotter than RN2C), hoping to extend plug lifetime which is 2 -3 rides currently.

Spooge has also leaked from the drain plug (left side), and from the spark plug hole. Oil level remains the same. This bike is know to foul plugs, and mine has less than 2k miles on it so I would be surprised if the problem was caused by a broken part. I am looking for a fix, it 'is starting to become expensive to replace those plugs.

Posted by: julien_d---------------------

Champion plugs? Each to his own I guess. Going one step hotter should help. Removing the airbox lid should also help. Actually jetting it will definitely help.

Posted by: whenfoxforks-ruled---------------------

Back in the day, word was Champion plugs stripped out spark plug holes, Japanese hole and American plugs, made bar room sense. NO, it was the half inch breaker bars and crooked plugs! Still, not a fan, and have never had any luck with Champion plugs in 2 strokes. The petcock had nothing to do with your spooge, an epa or fire hazard YES! You will get NO horsepower gains moving the power band around similar to a mx bike. BUT you will for sure need different jetting. Read the jetting sticky, multiple times. If you can do all the kdx to kx mods, you can jet the carb! If it seems the jetting changes are not doing what they are supposed to be doing, there is a defective/mechanical reason some where else causing the spooge, it could even be the way you ride it. Spooge is not un-burnt oil, it is un-burnt FUEL. Running leaner pre mix ratios is reverse/ bar room engineering. Vintage Bob

Posted by: SS109---------------------

Yep, get to jetting it right and ditch those Champion plugs!

Also, from all the reading I have done, the KDX250 really needs a different slide than stock, a #6 instead of a #5. You can mod it yourself if your up to it or send it to Ron Black and he will do it for $15. Here is a pic I stole from TT that shows the #5 on the left and the #6 on the right. Notice the bottom cutaway. You can easily see that there is a huge difference between the two. If you want to read more about it here is the thread I stole the pic from: KDX250 jetting problems

Posted by: GhostofSilverider---------------------

RE: proper jetting ... I can't go any leaner I am afraid,
again it's stock with a 152 mainjet, the pilot I didn't check because I could not remove it but I believe stock it's a 38 . I do not think you can get smaller jets for that carb, but the thing is since the pipe was opened up I should be enriching , actually the pipe annd airbox mod call for changing the mainjet to a # 165, from the info I gathered on that specific bike in a 1992 magazine article. Obviously if I enrich here ,, my problems are only going to get worse. One thing that could explain what I experience is if the pilot jet was not a 38 and was too rich.

Posted by: SS109---------------------

Jets are available for the PWK in a lot of different sizes ranging from an 80 up to a 230 main and pilot jets from 35 to 80.

Why can't you go leaner? Because stock was a 152? If you are still fouling plugs then you need to go leaner. It is as simple as that. Do you know how to jet a bike by correctly reading the plug?

The KDX250 was known to be very rich from the factory so going to a smaller main/pilot and/or to a leaner slide are all proven things to get the bike running well. The big thing is the slide which I already pointed out to you. Did you happen to read the thread I linked to so you can get the benefit of many other KDX250 owners experiences and how they solved the problem?

BTW, just an FYI, I too own a KDX250.

Posted by: whenfoxforks-ruled---------------------

Quote:

Originally Posted by GhostofSilverider

RE: proper jetting ... I can't go any leaner I am afraid,
again it's stock with a 152 mainjet, the pilot I didn't check because I could not remove it but I believe stock it's a 38 . I do not think you can get smaller jets for that carb, but the thing is since the pipe was opened up I should be enriching , actually the pipe annd airbox mod call for changing the mainjet to a # 165, from the info I gathered on that specific bike in a 1992 magazine article. Obviously if I enrich here ,, my problems are only going to get worse. One thing that could explain what I experience is if the pilot jet was not a 38 and was too rich.

There you are, problem solved.

Posted by: David_L6---------------------

I don't know anything about the KDX250 motor, but a CR250 will foul plugs if it has a bad crank seal. Just an idea........

Posted by: whenfoxforks-ruled---------------------

Quote:

Originally Posted by David_L6

I don't know anything about the KDX250 motor, but a CR250 will foul plugs if it has a bad crank seal. Just an idea........

Not if you, get a MUCH hotter plug, reduce the premix ratio to boat specs, open up the air box and silencer, and most importantly, ride it very slow. Surely I jest? Vintage Bob

Posted by: julien_d---------------------

Quote:

Originally Posted by whenfoxforks-ruled

Not if you, get a MUCH hotter plug, reduce the premix ratio to boat specs, open up the air box and silencer, and most importantly, ride it very slow. Surely I jest? Vintage Bob

You jest? Sounds reasonable to me, lol.

Posted by: dirt bike dave---------------------

FWIW, I used to run a B7ES on my KDX250 and the jetting was leaned up substantially from stock, including a slide with more cutaway.

No signs that the B7 plug was too hot, though I would occasionally use a B8ES for long dual sport rides with lots of highway.

Posted by: whenfoxforks-ruled---------------------

Quote:

Originally Posted by dirt bike dave

FWIW, I used to run a B7ES on my KDX250 and the jetting was leaned up substantially from stock, including a slide with more cutaway.

No signs that the B7 plug was too hot, though I would occasionally use a B8ES for long dual sport rides with lots of highway.

Exactly. How it is being used, tune and jet accordingly. Some riders can get away with a really lean premix, and still have adequate oil protection for their usage. A more aggressive rider/usage would melt the motor, set up like that.

Posted by: Tom68---------------------

Steel tank model, looky here. http://www.dirtrider.net/forums3/sh...&highlight=carb

Posted by: G. Gearloose---------------------

Firstly, as been said, Friends don't let friends run champions.

And honestly, how much time do you really spend on the main? You can change it all day, won't stop the spooge but can frag the engine.

First Set the main with some WOT runs on fresh plugs. Don't be freaked out from a white insulator, that means its cleaning itself like it should. Grey is what is bad. Then leave it be.

Then set the needle for best clean midrange. This is where your going to net something

Then set the pilot and AS for best low and off-idle.

I've found, from experience and what i've learned here, an engine jetted to a B8 is right on. Throw a B7 in the same well tuned engine and you can hear preignition somewhere. Jet to a B7 you will end up phatter than neccessary, and its just wasted power, since heat is power.

Posted by: GhostofSilverider---------------------

What's wrong with Champions plugs ?

Actually a Champion RNC 3 seems to be the solution to my problems . I put that plug in, and it 's still running strong after 5 rides (although short ones) the NGK B8ES couldn't go past 3 . There was some kind of defect on the plug ( a small protruding piece of metal on the tip of the electrode which a mechanic removed with sand paper) other than that I love that plug and will order a replacement soon, but it's hard to find. The Champions RNC 3 is the equivalanet of the B8ES as far as I understand , yet, it's not wet when I take it out, it's not greasy, some parts black some parts light brown with shades of black. Must be hotter maybe. The bike runs great with it anyway.

Why should I go back to NGK on that bike ? For now until I have time to finetune the jetting , this seems to be the miracle solution, even if it fouls tomorrow , it has a longer lifetime and appears more reliable (some of the 4-5 NGK I used before died after 2 short rides around the block). The previous owner also used a Champion, (older and colder NG2 model = RN2C) and it lasted some time too.

Posted by: EYY---------------------

Try to really focus on jetting. The plugs aren't the problem, so changing types won't be much help. I'd definitely try going slightly leaner on both the pilot and main. Especially the pilot. Have you checked how many turns out the mixture screw is? Checked the float height, needle and seat condition, all of that stuff?

The problem may even be mechanical or a fault in the ignition system.

Good luck

Posted by: motopsycho87---------------------

There ain't nothing wrong with the plugs! Champion are just as good as NGK, if they weren't they wouldn't still exist!

Is the bike actually running correctly? If so I really would suggest jetting.

Check the plug gap is correct.

Plugs can make a different though, if it is getting fouled (AFTER JETTING CORRECTLY) you need a hotter grade plug, And for a teeny weeny performance enhancement, buy a triple electrode spark plug, it takes up a tiny bit more space in the head (thus increasing compression a tiny bit) and you get a larger spark area creating better spark conditions!

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KDX 250 still fouls plugs

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