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Bike runs great then just dies

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Okay, I'm completely baffled on this one. To make a long story short, my 06 KX250F lost all the radiator fluid and almost siezed. I shut it down when I realized what happend but it was too late. I superheated the bike. Piston and cylinder were shot and the exhaust valves were pitted. A shop replaced the valves and I replaced the cylinder and piston with a Athena 290 kit (why not, right?) I adjusted the valves and put everything back together and it fired right up. I test rode the bike and was super pumped on how well it performed with the 290 kit. About 20 minutes into the ride, it just died like the fuel was off. No luck on starting it right away but after 5 minutes, it fired right back up. 10 minutes of riding and it just died again. It did this about 3 more times while making my way back to the truck. Always fired up after 5 minutes or so and ran great until it just died again. I figured the carb must be dirty so I pulled apart the carb cleaned it and put it back together. I test rode it again and the bike was great, chugging up hills, snappy power, then it just died. It fired right back up this time, ran, then died. Spark plug was a little white and since it seams to die at low RPM I richened up the pilot air screw. Didn't help and was actually worse. I leaned the screw 1/4 turn and didn't help and was still worse. Now the bike won't stay running for more than a minute, but fires right back up after it dies. There has to be something that I did that would be causing this. I didn't touch the electrical system so I can't imaging the CDI would be toast already unless it is just a coincidence. What kills me is how well the bike runs right up until it dies so there are no symptoms to go by. Any help would be greatly appreciated. Sorry about the long thread but I wanted to give as much detail as possible.

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I would test the stator. Heat like that can destroy the stator and may only show up when the engine heats up. After several heat cycles it can completely kill it. I would run the engine until it dies then check for spark.

How are the valve clearances? Did you check head warp?

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Valve clearances are good and no head warp. I thought about testing for spark right after it dies, but now it fires right back up so it's definitely getting spark at least after a few seconds of rest

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Well...could be several different causes. I always try the simplest and easiest checks first. Like the wiring and connections for the kill button, and the fuel vent line, and the floats. Then maybe the plug wire, CDI connections...your airbox doesn't have a shop rag stuffed in it, does it? (happens alot!)

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All wiring connections appear good at least by visual inspection and tugging here and there. Fuel vent is functional (died with the gas cap off). No shop rag (he, he). Again, it just runs so great over whoops, hills, sand, whatever, then just dies with no warning.

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The stator sounds like a possibility but would it just cut out with no warning or would the bike be running poorly first?

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clean ur carb angain because its probably not getting enough fuelor your jetting might be wrong for the 290cc kit.also just check ur spark because it might be weak.

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And you have changed out the plug, right?

checked the fuel filter?

made sure the floats are at the right setting?

hmmmm.....with it running on the stand, if you spray wd40 all over the intake boot and the idle speed surges, that would indicate an air leak...

Has the bike actually idled since the rebuild?

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Bike idled since the rebuild just fine like nothing was wrong. Plug is new fuel filter is clean. I did not check the float setting but I didn't change anything there and I think it would be bogging in turns or whoops. That said, I pulled the stick coil and the outside is all melted. It also zapped me just holding the outside of the coil. Is that supposed to happen? I think it should only send a spark through the tip to the spark plug. Yes?

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Bike idled since the rebuild just fine like nothing was wrong. Plug is new fuel filter is clean. I did not check the float setting but I didn't change anything there and I think it would be bogging in turns or whoops. That said, I pulled the stick coil and the outside is all melted. It also zapped me just holding the outside of the coil. Is that supposed to happen? I think it should only send a spark through the tip to the spark plug. Yes?

Sounds like you've found the culprit. Or are at least getting very warm (no pun intended).

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