main jet to big???

kdxmann · Jun 23, 2003

i have an 01 kawasaki kdx200 and i was driving it back to my house and got to a big straightaway so i went up to third gear and when i gave it full throttle the plug fouled and the engine died this is the secound time this happened is my main jet to big. i dont know of the carb set up beacuse i didt touch anything once i bought it used from the dealer it has a pc pipe and silencer im thinkin the main jet is rich i do know it is running a stock spark

fatty_k · Jun 23, 2003

Sounds to me like a main jet problem. If it is fouling plugs you may need to go down more than one size.

jamin326 · Jun 23, 2003

you bought it used and you didn't rejet it, if i was you i'd take that carb apart and rejet

kx200 · Jun 23, 2003

One time I was riding Six Days of Michigan and had the main jet fall out on my KDX you can still ride it but only up to ¾ throttle. It’s not that hard to get the main Jet out just remove the bolt looking thing on the bottom of the float bowl to get to the main jet, you don’t need to take it off the bike.
Good luck

procircuit21 · Jun 23, 2003

How the heck did your main jet fall out?!

canyncarvr · Jun 24, 2003

Check HERE for basic jetting information.

The same link is referenced in the 'Every kdx rider should read...' post stuck to the top of this board.

If you haven't '..touched anything...' after buying it, you should.

...or carry a bunch of plugs for spares, have your bike run for crappola, smoke like crazy and blow black goo all over the place.

Your choice.

kdxmann · Jun 24, 2003

it runs fine at low rpm but everyother time i run at high rpm i have to shift at like 3/4 throttle maybe it just fell out.ill check tomorrow. how many sizes should i go down like 2 or 3

canyncarvr · Jun 24, 2003

Click here to go to a thread that will direct you to a website that will give you a good deal of jetting information.

It's in the 6th post down from the top.

I'm gettin' dizzy!! ;)

motometal · Jun 24, 2003

your main jet is probably too big, i'm not disagreeing with the previous posts. 

Just throwing out a theory of mine...I think some times, especially if the lower-speed circuits are a bit rich, the premix oil separates out and builds up in the lower end of the engine around the crank.  It collects there until you whack the throttle open, then it fouls the plug.  I have had this happen even on bikes which were jetted fairly lean, such as when giving rides on my CR.  I make a point of cranking the throttle open in 3rd or 4th gear once the engine is warmed up (assuming there is room to do this).  Once the bike is warmed up and cleaned out, there won't be any problems with plugs unless I putt putt for extended periods of time.

kdxmann · Jun 25, 2003

im going to buy 5 leaner main jets to figure out which one works best. what type of sound and feeling would i get if its to lean?what sound and feeling should i get if it is right on? thanx

motometal · Jun 25, 2003

another way to learn about the main jet is to (after the engine is warmed up) hold the throttle wide open in nuetral.  If it sounds like it will rev to the moon, let off...it's either just right or on the lean side.  I suspect what you will find, at least before leaning the main, is that it doesn't rev very far before it just sputters and won't rev any higher.  This indicates it's rich on the main.

Another thought-lean the main one step at a time, if it makes a good improvement in wide open acceleration than you are probably ok.  If you get to a point where you went one step leaner and couldn't tell any difference (or it actually got slower), you should backtrack one step.

This is not an exact science, and most of it comes down to just listening to what the bike is telling you.  If you use good fuel, there will be much less chance of actually hurting the engine if it does end up on the lean side.

kdxmann · Jun 25, 2003

i will try that thanx for all the help

canyncarvr · Jun 25, 2003

Hold the throttle wide open with the bike just sitting there in neutral if you wish.

Do that to my bike and I'll have to kill you. And I'm not even kidding.

Holy cow! The condition of the spark plug is the way you check a main jet. You obtain that with a wide open throttle plug chop test (described on CDave's site). Note this operation requires the bike be under load

Check that 'look' out here .

This sounds like a disaster just itching to happen! I suggest a bit of research on your part to verify generally accepted technique.

kdxmann · Jul 3, 2003

i know its been awhile but when i went down to my local motorcycle shop he told me that the main jets are imn intervals of 5. my main jet was stock so im guessing that the guy before me didnt jet it correctly. i put 155 main and i think that should do it.doany of u guys have like a 158 main jet or something like that because always thought they went in intervals of one.is it easy getting to the needle jet. and is the pilot jet to the left of the main jet or wat? thanx jeff

G. Gearloose · Jul 3, 2003

Originally posted by kdxmann
i know its been awhile but when i went down to my local motorcycle shop he told me that the main jets are imn intervals of 5.

Those jabronies are always good for a few yuks! :silly:

it goes 2-3-3-2-etc

MX175 · Jul 3, 2003

C'mon CC, don't you do that WFO in neutral jetting check on every bike you borrow? It also helps to stir up the oil in the crankcase and gets the water pump good and primed, and loosens up the reed valves. I always do it, but I wonder why no one lends me their bikes any more.

Let me get my tongue out of my cheek and thank-you for offsetting some of the insanity the can occasionally be found on this site.

motometal · Jul 4, 2003

wow, wake up people!   Have you ever noticed that in a lower gear, the engine will only rev so far, even though there is minimal load on the engine?  If the jetting is on the lean side, yes it could rev up pretty high if you just leave it wide open, but if you read my post again you will note that I said to let off.  Really this is no different than many people's warm up technique, only it involves holding the throttle in a fixed position for a second or two to see how it responds.  This is a great method because it works and doesn't require any wrenching.  It was shown to me by a professional tuner (but i'm sure he's just an idiot) :moon: .

By the way, when is the last time you heard of a two stroke having engine problems due to being over-revved?  Most of these engines are capable of handling higher rpms than they are capable of revving.

Reading the plug will work, but just like the method I described, if you don't know what you are doing, it's worthless.  The method many people use to read the plug really only tells you how hot the plug is running, not specifically how the bike is jetted.  You really need to look at the fuel ring on the plug which requires a lather or some type of saw to disect the plug.  If you wish to learn more, try a search on reading plugs.

wibby · Jul 4, 2003

On my '92 the "main" needs a socket for removal, the pilot uses a flat bladed screwdriver.
I've even included a pic, the main is on the right

From Canadian Daves Tech Tips, Carburator Tuning:

Available Keihin Jets – There’s a list of available main and pilot jets for your reference. I’ve included jets sizes commonly used to fine tune PWK equipped KDXs. This includes 1988 to 2003 KDX200/220 as well as second generation KDX250s. There are larger and smaller sizes available that aren’t listed here. This list might seem rather long but it includes possible jet sizes for a number of temperatures, altitudes as well as modified cylinders.

"21 Series" Pilot Jets - 38,40,42,45,48,50,52

" 13 Series " Main Jets – 140,142,145,148,150,152,155,158,160,162,165,168,170,172,175,178,180

main jet to big???

kdxmann

fatty_k

jamin326

kx200

procircuit21

canyncarvr

kdxmann

canyncarvr

motometal

kdxmann

motometal

kdxmann

canyncarvr

kdxmann

G. Gearloose

Pigment of ur imagination

MX175

motometal

wibby

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main jet to big???

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