KLX250S cuts out and won't run after WOT

Discussion in 'Thumpers' started by Rob.G, Mar 21, 2013.

  1. Rob.G

    Rob.G Mostly Harmless

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    This is damn weird. I've run out of ideas. It's done this three times in the past two weeks.

    The bike would run just fine until you go Wide-Open-Throttle. After that, once you release the throttle, it sputters and dies. It will restart, and it will idle. But trying to give it any throttle and it dies instantly.

    The first two times it did it, I figured the carb was dirty, so I pulled it, disassembled, sprayed it out, reassembled and reinstalled, and it was fine. But of course it did it again. Did the same spray job a second time. Back to running again. I rarely go true WOT so it's not like it works fine for a while and then starts acting up.

    This past weekend, it did it a third time and I coasted to a stop at the base of the big bridge as cars behind me started honking like the a-holes that they are. On the side of the road, I got it idling, turned on the choke, it'd idle up around 5500 RPM (usually it'd be at 4000), and about the time a cop showed up to see if he could help, it decided to behave again. So I thanked him and road home.

    But, as I approached home, I decided to go WOT again and see if it'd do it again. And it did. So I coasted home and parked it. Yesterday, at the recommendation of a friend, I pulled the carb and disassembled again, and put it in a brand new can of Berryman's carb soak stuff (the gallon bucket) and let it sit for 24 hours. Tonight, I finished up the carb, sprayed it out good with carb cleaner, and put everything back together.

    This time, no luck. Same as before. It'll start, and it'll idle. Give it any gas and it dies. Now, being here in the garage and not on the side of the road, I played around with it a little. I found if I VERY gently roll on the throttle, I can get it up to 3000 RPM (it idles around 1800), but it sputters and coughs badly, like it's missing. Anything more than about 1/4 throttle or 3000 RPM and it dies. I made sure the gas is draining properly into the carb from the gas tank, and it's brand new gas just bought two days ago. The spark plug is just over a month old.

    Since this problem had only been appearing when using WOT, I can't help but think it could be electrical. CDI or coil maybe? I dunno. Even my friend is stumped at this point.

    I've checked all the electrical connectors and they seem to be fine. The diaphragm in the carb is like new. The bike is a 2010 and only has 3400 miles on it. The air filter is clean (I just cleaned it two days ago). All the carb boots are fine, also like new. The carb vent tubes aren't kinked. There is no TPS on the carb. It's a very basic Keihin CVK 34.

    Like I said, I'm out of ideas. Anybody ever seen a problem like this before?

    Rob
    #1
  2. qkenf4u

    qkenf4u Been here awhile

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    so it will stay running with the choke on ? seems funny that a warmed up bike will rev that high after being warmed up.....usually adding choke to a hot/warm motor kills it.....

    get it to act up again and once you have it started add choke and try to rev at the same time.. if it will rev fine with choke then maybe a partially plugged pilot ??
    #2
  3. D_A

    D_A Long timer

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    It really does sound like a fuel problem. Make sure your petcock isn't blocking up or losing vacuum or something as well.
    #3
  4. Rob.G

    Rob.G Mostly Harmless

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    Yeah it'll run with the choke on... always has even when warm. And it won't rev with the choke on either.. does the same thing. But usually with the choke on, it idles at 4000 RPM... but with it acting up, it idles at 5500. I find that a little odd too.

    Fuel is definitely flowing from the tank. I can fill the carb up, remove the tank, and start the bike (like, say, when you shut off the petcock to run the gas out of the carb for storage), and it'll still do the same thing.

    Rob
    #4
  5. FlyingFinn

    FlyingFinn Long timer

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    Sounds not getting enough fuel.

    To check proper fuel flow from the tank, hook up the tank normally, open petcock and then open the float bowl drain screw.
    Do you get good flow for as long as the screw is open, say for a minute?

    While there, check the fuel level.
    With a clear hose attached to drain spigot, turn the hose straight up along the side of the carb. Now SLOWLY open the drain screw.
    How high up the hose does the fuel level settle? It should be about level with the float bowl gasket.

    Mikko
    #5
  6. Ranger Ron

    Ranger Ron Been here awhile

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    Have you checked the filter in the carb inlet tube?

    Ron
    #6
  7. fritzcoinc

    fritzcoinc Enjoying my last V8

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    Are you using the correct heat range spark plug for high speed? look in your owners manual.
    #7
  8. rickcj7

    rickcj7 Been here awhile

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    Make sure the tank vent isn't plugged or kinked
    #8
  9. IceBikeDave

    IceBikeDave Been here awhile

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    Rob,
    My KLX did that EXACT same thing as you described. I fast idled (on choke) it home and I found the problem. The throttle slide was stuck in the up position. It ran great full throttle at 9000 RPM, then, just as you described. So what made the slide stick in the up position? When I changed the jet needle the last time, I didnt align the top of the slide spring to go around the three bent sheet metal tabs on the slide top cover. The spring went around the outside of two tabs and inside of the other tab. I re seated the spring and all was well. I then deliberately mis-seated the spring to see if I could make the problem happen again. I fingered the slide to the up position and it hung in the up position. I look very closely at that spring top before I screw down the carb top.
    #9
  10. Rob.G

    Rob.G Mostly Harmless

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    Update:

    I found a vacuum leak. When I de-smogged it, I had put a vacuum cap over a 1/2" pipe coming out of the front of the motor, per de-smogging instructions. I decided to remove the cap, which looked fine, just to be sure. Once I removed the clamp, I could see a big tear. So I replaced it with a much better cap. I was all excited thinking I had solved the problem, but it's still doing the same thing.

    Per other instructions here, I tested the flow out of the tank, and out of the carb from the bowl drain. I pulled the tank petcock and cleaned it thoroughly (it wasn't dirty). With the bike off, I do get a small stream out of the float bowl. I wouldn't call it a lot, but it's a decent amount. I've had floats stuck on carbs before and it wasn't that much, so I can't say with an certainty that it's getting enough fuel from the tank. I haven't been able to find any clear tubing small enough to check the float level; gonna have to hit Lowes or Home Depot for that, which is a trip clear across town. Maybe tomorrow I can do that.

    Ummm.... there's one in the inlet tube??? It sure doesn't look like there's one there.

    I looked at the parts fiche. Yep there's one there. Does it go way down in there, like a suppository or something? :) I know I sprayed carb cleaner in all of the inlets and watched it spray out all of the other tubes and stuff.

    This is an interesting idea. I'll have to go pull the [expletive deleted] duct hose out again and look in there and see. I suppose it's possible, but I know for a red dog fact that I put the spring back in properly, because I took it apart a second time to be sure. But we'll see. Maybe something else is making the slide stick. If the thing was stuck right now, would it start and idle?

    It's just weird that after soaking and reassembling the carb that it'd still be acting up... like it'd at least work fine after reassembly and then stick if I got WOT again.

    Hmmmm.

    Rob
    #10
  11. IceBikeDave

    IceBikeDave Been here awhile

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    Rob,
    Mine would start right up and idle fine, but after just a tiny amount of throttle it would run bad and die. Just saying. I didn't have to pull the inlet duct to fix the problem, just to verify the results. Like the old guy said,"If you cant make the problem come and go, you didn't solve the problem".
    #11
  12. Rob.G

    Rob.G Mostly Harmless

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    Okay, I just went out there and took the top off the carb. I removed the slide, re-checked the needle, and reassembled. I am now 100% sure I got the spring in correctly. And unfortunately, no change.

    Rob
    #12
  13. IceBikeDave

    IceBikeDave Been here awhile

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    Rob,
    Interesting problem you got there. Just for fun, next time you take the carb off the bike, put your shop vac on the carb spigot and watch the action of the slide via the air cleaner side. To prevent even more fun, drain all the gas first.
    #13
  14. IDRIDR

    IDRIDR Take me to the River

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    :rofl


    Interesting problem Rob. Been following along...wish I had some good advice for ya.
    #14
  15. DYNOBOB

    DYNOBOB lucky dog

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    How high is your needle raised in the slide? Maybe the needle is rising out of the hole at WOT and getting stuck on top. It does sound like the slide is sticking up, bike would idle somewhat normal as long as the throttle blade is closed and go dead rich as you open the throttle. Maybe try the stock needle/spring? Could you have gotten bad gas?

    good luck




    .
    #15
  16. bdcorrigan

    bdcorrigan Been here awhile

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    I know it is not the same bike but my XL600 did the same exact thing to the T and it was electrical, my stator was going bad. Tested it, it was bad and replaced it and bike ran wonderful. I would check the electrical just to be on the safe side.
    #16
  17. bryantjt

    bryantjt Long timer

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    With the carb on the bike, or even holding it level, reach in and push the slide up and watch how it returns. It should come back fairly quickly. Also, check the action with the shop vac as suggested.

    My 2006 KLX had 9000 miles on it when I traded it in and I had spoken with the dealer after that. Apparently a month or so after a guy bought it, the cdi cracked and got water in it. Have you looked at your electrical at all?
    #17
  18. Rob.G

    Rob.G Mostly Harmless

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    The problem has been isolated. Not corrected, but isolated.

    A friend came over tonight from out of town with his 2012 KLX250S. I had promised him I'd rejet his carb for him, and after doing so, we popped it on my bike. Bike fired right up and ran perfectly. So... it's definitely something in the carburetor.

    We put his carb back on his bike and it's purring along nicely. So now, I need to figure out WTF is up with mine. I think I'll do the shop-vac test next, because I compared his slide movement to mine and they appear to be identical.

    Rob
    #18
  19. Rob.G

    Rob.G Mostly Harmless

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    IT'S ALIVE!!!!!!!!!!!!!!!!!!!!!!!!!!!!

    I got home today after (successfully) completing my Dirt Bike Instructor Training, and was beat. The more I sat here at the computer, the more I wanted to just go to sleep. Seeing as it was 5 PM, that wasn't a good idea. So I decided to start doing stuff. After washing off the DR650, I went in the garage and glared at the KLX's carburetor.

    I picked it up and looked it over. I tested the slide again. It was working fine. WTF was its problem? I saw something that didn't look quite right. I THOUGHT it was, but I wasn't 100% sure, so I pulled up the parts fiche. Take a look below:

    [​IMG]

    Look for the main jet. Now go up two parts to the one marked 16017. See that little fucker? I had inserted it from the top, as in, from within the barrel of the carb. I thought that's how I remembered it coming out, but I wasn't sure because it was sticking up farther than I seemed to recall. So I confirmed it on the fiche that it was in wrong.

    Off came the top and bottom of the carb, and I moved it back into its correct position and reassembled.

    I popped the carb on the intake boot, hooked up the throttle, added some fuel, and tested it. Holy crap, it worked! It revved freely. WTF. I don't see how that could have caused the problem, but I won't look the Fuel Gods in the mouth. I reassembled the bike and decided I needed to go for a ride to see if the problem returned after going WOT.

    I geared up halfway, hopped on and went for a quick ride. Up the street a bit, then a U-turn, so if it died, I was aimed downhill. I wound it out in 3rd and 4th gear, and also went WOT in 5th and even 6th (which on a 250 isn't really saying much), and then the moment of truth... hop into the middle lane to turn left, let off the throttle... coast... coast... coast... come to a stop.... it's still running... give it a little gas... it was doing ok.

    So... at least my initial test is positive. I did feel a very slight stumble at higher RPM, but that could have just been from tapping the rev limiter. I will experiment more tomorrow and if the thing keeps running, I'll stick my Wideband O2 sensor on it and doublecheck my jetting. I ended up putting a 124 main jet in Cory's KLX last night, but there's a 120 in mine and we have identical mods. And frankly his feels faster. So who knows, maybe I need a 124. I'll figure that out tomorrow if it continues running.

    If it continues to run properly, my thinking is that there was crap in the carb, possibly some less than perfect gas, and it was still gummy from having sat for a few months unused. It's just coincidental that it would act up the same way after reassembly, with my slightly incorrect positioning of that one part. At least that's my theory. :)

    Thanks to everybody for their input! It's very much appreciated!

    Rob
    #19
  20. brieninsac

    brieninsac Been here awhile

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    What an ordeal! Glad you found the culprit. It's funny how sometimes it takes a day away from something to get that ah-ha moment.
    #20