Plug fouling on a 250, compared to a 125 ?

[kimoajaj]

Hi everyone!

I`m selling my 1993 KX125 ( :( ) in order to get a newer bike.

First I was thinking of a 250 fourstroke, but I think it will be too expensive for me. I have therefor decided to go for a 250 two stroke.

I`m wondering if plug fouling is a common problem on the 250`s or if it`s more normal on 125`s ?. My old KX tended to dislike not being pinned everyother minute, so I basically had to ride it somewhat "hard" in order to avoid plug fouling.

A friend of me just got an RM 250 1997 and he`s had no problems with plug fouling, and he doesn`t ride hard at all.

I`m thinking of a 2001 KX250.

My reason for wanting a new bike is:
* better suspension, so that I can jump higher
* more low end power, I`d like to learn to wheelie and my 125 was abit to "exploding", if you see what I mean
* I don`t want to think of the plug fouling all the time.
* the newer bikes looks better !! :)

Well, hope someone can give me some advice or info on this, I`d appreciate it:).

Thanks.

Joakim, Norway

 

[Brian_V]

I've got an 03 KX 250, and don't have fouling problems. I used to until I got the jetting and premix sorted out. I ride a lot of tight woods, and like to run it low in the rpm range for a lot of that. As long as I goose it every once in a while, no problems. The only time I think about it is on long technical downhills, where I just clear it out every couple minutes. Sure, if I let it idle too long with the choke out it will foul, but I don't have near the problems that you report. That being said, I don't think it has anything to do with 125 vs 250. I think it's more jetting related.

 

[YZ165]

I don't think it has anything to do with 125 vs 250. I think it's more jetting related.

:nod: Yer a pretty smart fella' Brian! :cool:

 

[bikepilot]

Yep, jetting related and no more. I've owned 2-strokes from 80cc to 500cc and have done loads of tight slow trail riding on all of them and never have had a fouling problem.

 

[KX02]

Yep, jetting related and no more. I've owned 2-strokes from 80cc to 500cc and have done loads of tight slow trail riding on all of them and never have had a fouling problem.

If I ride really slow stuff I still get some drool out of my exhaust vs. more wide open riding. I hesitiate to go any smaller on the pilot jet for fear of being to lean. Do you think that the drool is caused by the bike not being ridden hard enough or do you think I should try leaner yet on the pilot? :think:

 

[kimoajaj]

Ok guys ! :). After I posted this thread I did a search on fouling and I imediately understood that the answer I would get was "It`s jetting related" :).

So I guess I have to read some more about jetting. Is it possible for novise to jet a bike so that it becomes suitable for the riding it will be used for?.

 

[bikepilot]

Ok guys ! :).
So I guess I have to read some more about jetting. Is it possible for novise to jet a bike so that it becomes suitable for the riding it will be used for?.

Yes, try a search for jetting tips and don't be scared to experement. Unless your running wide open, high rpm for an extended period of time you will not be able to hurt anything should you go too lean, though you will notice a decrease in performance/rideablility and will want to go back a step richer.

Assuming your too rich now try dropping the needle one notch and going one size smaller on the main jet for starters.

 

[bikepilot]

If I ride really slow stuff I still get some drool out of my exhaust vs. more wide open riding. I hesitiate to go any smaller on the pilot jet for fear of being to lean. Do you think that the drool is caused by the bike not being ridden hard enough or do you think I should try leaner yet on the pilot? :think:

Most of my bikes will drool a little with lots of slow speed riding. Its really nothing to worry about imo. I doubt the pilot is the source of the problem, typically low speed riding is done at low rpm's and moderate throttle openings, the pilot only really deals with very low throttle openings.

I'd focus on the needle and possibly main. That said, there is no need to fear going too lean, if you do get too lean, you'll notice it running poorly and can always change back. You certainly will not be able to damage anything with a lean pilot. Really, the only way to do any permanent damage with jetting would be to get the main way way too lean and run full throttle, high rpm, high load for a long time. Don't be afraid to experiment with different jetting setups till you find something you like. If you think its a bit rich go ahead and try dropping the needle a notch and turning the air screw out a bit. If you end up with more than the recommended turns out on the air screw to get it where you want it put in a smaller pilot. If its still rich with moderate to open throttle go with a smaller main. Remember that which jet determines the mixture is dependant on throttle opening, not rpm or engine load. So even if your going slowly at low rpm, if your throttle is being opened a good amount your operating primarily off the needle and main.

good luck

 

[KX02]

Thanks! I will play around some more with the jets. I have a leaner JD needle I am going to try too, but probably not until next summer as the weather will be getting alot colder soon here in Ohio.

 

[AST]

kx02, what size pilot are you running with the jd kit? In my 05 kx250 I dropped it down to a 45 with the jd kit. I could have went down to a 42 but I added boyesen reeds and that leaned out the pilot series a little bit so I left it there.

 

[KX02]

AST, yes I installed the 45 that came with the JD kit. It was still pretty rich so I did go to a 42 pilot and that seems to be pretty close depending on the temp. I am jetting according to the method's described by the Maxima jetting guide and the bike does run great but the last times I've ridden have been in tight woods and a tight track where I was really not opening up the bike.I still get some spooge, not alot, out of the silencer. According to the Maxima jetting guide 99% of spooge is caused by the pilot being to big. So my question was should I go even leaner on the pilot or is it just because I am not riding hard enough? :think:

Are you running a stock pipe? If not how would you compare any aftermarkets you have tried?

 

[AST]

I am running the pc pipe and silencer. That and the jd kit and boyesen reeds are the only thing I have added. The 05 motor rips my arms off! :nod: