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Old 03-21-2013, 09:05 PM   #1
Rob.G OP
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Joined: Jan 2010
Location: Fulltiming in an RV!
Oddometer: 2,050
KLX250S cuts out and won't run after WOT

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
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Old 03-21-2013, 09:31 PM   #2
qkenf4u
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Location: nice warm bike riding COTTONWOOD ARIZONA...
Oddometer: 201
Question

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 ??
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Old 03-21-2013, 09:38 PM   #3
D_A
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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.
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Old 03-21-2013, 09:42 PM   #4
Rob.G OP
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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
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Old 03-22-2013, 02:58 PM   #5
FlyingFinn
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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
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Old 03-22-2013, 04:05 PM   #6
Ranger Ron
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Have you checked the filter in the carb inlet tube?

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Old 03-22-2013, 05:36 PM   #7
fritzcoinc
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Are you using the correct heat range spark plug for high speed? look in your owners manual.
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Old 03-22-2013, 05:50 PM   #8
rickcj7
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Make sure the tank vent isn't plugged or kinked
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Old 03-22-2013, 06:06 PM   #9
IceBikeDave
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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.
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Old 03-22-2013, 06:17 PM   #10
Rob.G OP
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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.

Quote:
Originally Posted by Ranger Ron View Post
Have you checked the filter in the carb inlet tube?
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.

Quote:
Originally Posted by IceBikeDave View Post
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.
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
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Old 03-22-2013, 06:22 PM   #11
IceBikeDave
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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".
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Old 03-22-2013, 06:33 PM   #12
Rob.G OP
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Quote:
Originally Posted by IceBikeDave View Post
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".
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
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Old 03-22-2013, 06:50 PM   #13
IceBikeDave
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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.
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Old 03-23-2013, 10:08 AM   #14
IDRIDR
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Quote:
Originally Posted by IceBikeDave View Post
To prevent even more fun, drain all the gas first.



Interesting problem Rob. Been following along...wish I had some good advice for ya.
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Old 03-23-2013, 10:17 AM   #15
DYNOBOB
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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




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