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Kx250f starts, stalls, won't start

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Hey guys, I just got a 2013 kx250f with three hours on a full rebuild and It has an issue where it will start cold, stall, then won't restart. Also, when I was able to ride the bike and crack open the throttle, the exhaust pops and makes no power and will occasionally stall, leading me to believe it's running lean. If it doesn't stall on idle, it will definitely stall off the clutch. What could this issue be? I checked the valve clearance and timing, all good. I have a good amount of experience wrenching on bikes, but this is my first EFI bike so I'm a bit stumped. Thanks in advance

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Simple things. New plug. New gas. Check fuel pressure. Recheck nothing is unplugged.

If it did run after the rebuild and now doesn't, you could have fried cams, valves, etc. Did you check all that and check movement when you had the valve cover off? What are you torquing your camshaft cap bolts to...should be 87 INCH pounds.

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Simple things. New plug. New gas. Check fuel pressure. Recheck nothing is unplugged.
If it did run after the rebuild and now doesn't, you could have fried cams, valves, etc. Did you check all that and check movement when you had the valve cover off? What are you torquing your camshaft cap bolts to...should be 87 INCH pounds.


Has fresh gas and plug, didn't consider bolt torque though. Could this seriously cause issues? I honestly ballpark it since I don't have one of those digital wrenches. Everything appears great in the top end but could definitely check for bent valves

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Tight cam cap is a common problem on KX250F. People overcrank them after checking valve clearance. On my 11, and probably on your 13, cam cap torque is 87 inch pounds. Guys will misread and crank it down in foot pounds, etc. Also one of the cam cap bolts is longer than the others. Doesn't affect running that I can tell, but still an important detail.

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Did you ever figure out what the problem was.  I am having the same problem and have done all that you have done here including changing the spark plug and the gas.  Now it acts like it wants to start the first time I try and kick it and then after that it does nothing.

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On 11/8/2018 at 4:24 AM, Scsman said:

Did you ever figure out what the problem was.  I am having the same problem and have done all that you have done here including changing the spark plug and the gas.  Now it acts like it wants to start the first time I try and kick it and then after that it does nothing.

Hey, did you manage to figure this out? I'm having similar issues.

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Hey, did you manage to figure this out? I'm having similar issues.

Have you tried starting it with the throttle wide open. If it fires then check your intake valves.

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3 minutes ago, Death B4 DNF said:


Have you tried starting it with the throttle wide open. If it fires then check your intake valves.

My bike fires with 2 kicks when cold. It can idle for 2 minutes and it will shut down by itself and then It won't let me kick start without choke.

I have another example: When the bike is hot, it will start with 1 small kick (in N), when I put into 1st while clutch is pulled all the way in, I rev it a little and it shuts down without releasing the clutch. I can ride it if I throw the clutch a bit and rev higher, but I never had this issue before.

also while riding, it randomly wants to shut down, like it's choking or not getting fuel. If I rev it, it goes back to normal. I've had this happen even in 5th gear going downhill without throttle, getting to the end of the downhill it lost power and shut down.

The first time I noticed something is wrong was when I went wide open in 5th gear and felt for a split second like there was a cut in fuel / air and then it kept going as normal. But since that day, it's been worse each time. Not sure what's the problem.

It's a brand new +30 hour 2018 KX250F. Never done valve clearance yet. Will do next week, but don't know if it's related, because the bike starts with first kick, but acting weird when riding.

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And it’s not throwing any codes? I’d check all wiring connections and the air sensor and connection. Also there’s a tip over sensor that went bad on my boys 450. Might check that.

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1 minute ago, Death B4 DNF said:

And it’s not throwing any codes? I’d check all wiring connections and the air sensor and connection. Also there’s a tip over sensor that went bad on my boys 450. Might check that.

Where do I see the codes? the red lights blinking? never noticed it...

It will show codes just by starting the bike or do I need to ride it and wait for the issue to happen?

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Check your manual. It will explain it better then I can. I’d check all the sensors. Air,crank, tip over ect. Sounds like either a loose connection or sensor going bad. Check the air sensor in side the air boot too. Clean with a sensor cleaning spray.

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