Hi folks. Just bought a 2014 KLX250 and it looks like a great bike. It has less than 600kms and because it was ridden infrequently, I think the pilot jet is clogged. It starts fine but even with an extensive warm-up, it barely takes any throttle without bucking and hiccupping like it's out of gas. Also stalls on take-off unless I rev it more than necessary.

I did an extensive search here and went through the FAQ and discovered tons of info. on jetting and learned that the bike is jetted excessively lean from the factory. Not surprising with today's emission standards.

The recommendations I saw might be more than I need, at least for the moment. I don't intend to do any performance mods, I just want the bike to run good. So if I just change out the pilot jet to a bigger one (#40?), drill out the fuel/air screw and open it 2.5 turns and shim the needle with a thin washer, is that sufficient to get a great running motorcycle? Or is even the stock main jet too small?

Any advice you can give this new KLX owner is REALLY appreciated. We've still got some warm enough weather ahead and I want to ride this thing.

 

Annnnnd , another purchaser of a barely rideable KLX... Once you verify fuel delivery to the bowl, you'll need to become a "CVK expert" before you'll be able to get your bike running right. You should start by studying @Dpippins stuff (exploded CVK diagram) and my link below on "CVK issues".. Once you can identify all internal parts, what can go wrong with them, how to set them up, and all other problems, you are ready to begin rebuilding your CVK.

Once running right, you can begin thinking about performance mods.

 

Thanks Klxster. I couldn't see your "CVK Issues" link.

Well, I doubt I'll ever become CVK "expert", but after going through the carb section on @dippins excellent site, I think I can manage the air/fuel screw drill out and set, pilot jet, main jet and needle shim. Again, I want to keep the bike stock, otherwise, at least for the foreseeable future. I'm OK with the stock power and I want to keep it quiet.

There seems to be some varied opinions about upping the pilot jet size, so for now I'll clean the stock pilot jet, turn out the air/fuel screw and shim the needle. Do I need to up the main jet size on an un-modified KLX?

EDIT: Klxster, found your link in in your sig line. Forgive the aging eyes.

 

Holy crap! Am I glad I found it. Another gold mine of KLX info. Haven't memorized (not sure that would even be possible anymore) but I'm a little more CVK savvy and will consult your notes as work on the carb. The info. on cap sealing/diaphragm positioning is something I'll pay particular attention to. I might not have got it right without reading your post.

 

If you are leaving the bike totally stock, there is no need to fool with pilot jets etc,

Good luck to you on your dismantling, cleaning, and reassembly. Go slow, do not "cut corners", get it right the first time, and you are DONE !
Decide not to fully disassemble, or forget to check a circuit, you'll do it all over again, and over and over, until you get everything done-up right..

 

Hints:
Don't forget the emulsion tube cleaning, and don't lose the needle jet or install it upside down. Be sure every single circuit pathway of the pilot jet system is functional - especially every one of the transition ports!
Make sure the diaphragm passes the "finger lift test" before stuffing the carb back in the bike - re-do/revamp the diaphragm seating and slide, over and over, until it passes the test. Never reinstall the carb until it does.

 

Read about the finger test on your post. Wouldn't have thought of that.

Honestly, this is a bit intimidating. I did some minor work on my DR650 carb, (drill out A/F screw, shim needle), and did a full cleaning of my DR250 carb, but this seems a bit more involved. Just getting to the carb on the KLX is a lot harder. I'll take my time and consult yours and @dippins notes and try to get it right.

I won't change jetting sizes, (for now at least while it's completely stock), but I'm thinking shimming the needle is a good idea. It's gotta be a very lean needle to meet emission standards and richening in just a bit with a #4 washer should improve rideability. Unless you know it's a bad idea, I'll put the washer in.

 

Shortening the needle moves the fueling curve to the left - as seen on a dyno AFR chart. There should be no problems in doing so in the manner you suggest. There will not be any actual performance benefits BUT the placebo affect could be huge.. So go ahead..

 

the placebo affect could be huge..

LOL... wouldn't be the first time I've been guilty of that.

So what is the best thing to do to richen the overly lean carburetion on an unmodified (no pipe, no airbox mod, no Marcelino timing adjustments) KLX250? If I just clean everything, it's still going to be too lean, right? That means long warm-ups, hotter than necessary temps. and likely some surging and possible stalling.

 

To answer your question - NO ONE has EVER dyno tested and posted AFR charts for a dead stock KLX. We have no idea what the fueling is on a stock KLX. For that matter, no one has any idea what ANY jet changes, needle changes, clip position changes, needle shimming, etc ACTUALLY does to fueling. Only my dyno derived lidless recipes have data/dyno verified fueling curves and results.


If you must, it is ok to go ahead and get the #40 pilot jet. When you do your carb tear down/clean, install the 40 and set the fuel screw to about 1.5 out (for sea level) ..That takes care of idle fueling control... If you want to mess with enrichening the entire fueling curve, get the K125 main jet and slap it in - but DO NOT shim the stock needle if you do the K125. Your fuel mileage will go down and power levels will not be affected enough to be "real", but with these mods, the placebo effect would be overpowering - bending your reality into a surreal fog of absurdity.. You'll come back here spouting all kinds of crazy crap - and I'll advise you to start sniffing glue..