09 KX450F died on face of jump...

Needing some help diagnosing whats going on with my bike.

I was riding at bostwick creek MX today in FL when my bike died on the face of a big tabletop. There is a sweeping right into a sweeping left and then a long straight into the face of this table. Its 4th hammered down and just as I hit the face the bike died. Somehow managed to save it and avoid a bad crash. Bike did not restart on landing. It did not lock up thankfully. I rolled off the track and the bike refired on about the 5th kick. Rode it 20 ft and it died again. Got it going again and lots of popping and generally running like crap. Got it back to the pits. Started looking things over and can't seem to find anything obvious (such as electrical connector unplugged) so After the bike cooled down a bit I went back out and rode around and it was still running a little funny after a few laps so I packed it up and headed home. Got home and removed the valve cover to inspect valves. Left intake is at .003" other wise all valves are in spec. Piston is nearly new with around 5 hrs run time.

I'm thinking I've got an electrical issue. Since the problem only seemed to occur when the bike got hot I'm thinking possibly coolant temp sensor is faulty. Or the tip over sensor has some issue and cut fuel and spark. Lastly I'm also considering the idea of the TPS being faulty and causing some issue. Any ideas?

Could bad fuel cause this problem? It rained on my way home from my last ride day before this one, maybe some water got in the gas and gas can?

Any help greatly appreciated.

Forgot to mention that the bike seemed to be running hotter than normal, from what I could feel through my gear and knee braces. Coolant level is good and no leaks. I guess it's possible that since the track is sandy that I was pushing the bike harder than normal and that contributed to the extra heat. Could the coolant temp sensor shut the bike down if the engine begins to overheat?

Make sure the gas cap is not clogged and that it's venting properly, I would try some fresh fuel as well.


Does it run fine after it cools down? check fuel filter and try new plug, could be bad stator. Check timing as well.

Edited by Kawikx450

Same type of thing happened to me... ended up being a dirty fuel filter. Pulled apart the pump, cleaned the filter/pump unit in clean gas in the bottom of an open clear gallon jug to see the dirt that came out, then put it back together. Bike was fine after that... Might want to check that air mixture plug of whatever it is called that runs from the airbox to the motor.

Check that your cam chain didnt jump a tooth.


I would think its more fuel starvation related 

IIRC, the 09 had an issue with the pump breaking inside the tank rendering the pickup limited or useless. Something about the pump's intake breaking off due to fuel slosh.



Can you tell me what your resolution was?  My '10 bike just did the exact same thing and that could have been a nasty crash.  Really appreciate it!!!!

after you have checked the engine out mechanically I would look at the electrical connections....especially the fuel injector connection located under and to the left of the gas tank . Sometimes the electrical connection starts to corrode and during high g-loads like a jump face the connection is stressed and stops working or is intermittent . If you do find a problem with an electrical connection you can temporary by pass with a hard wiring the connection to test ride. You really have to look hard at all the electrical connection by disassembling each one. Typically on one side or both they may look green from corrosion. Good luck. Let us know if you find something.

As stated previously, KISS. Keep it simple stupid! My plug had spark but apparently not enough. Put a new plug and ran perfect again.

At least I have a fully inspected and greased wiring harness!!

Thanks for everyone's input. I know most people fix it and never tell what it was. I did for the next guy

Sent from my iPhone using Thumper Talk

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