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Hey yall. My 2011 YZ450F won't start. The original issue was that the timing chain skipped after a weird backfire during a ride when I tried to kick start it after a cool down. The tensioner was probably the cause although I don't know why since it only had 20 hours of use from the factory. I replaced the chain, rebuilt the tensioner, and replaced all the gaskets during the rebuild. Once it was back together it would not start, so I checked for spark, fuel, and compression. Spark was good. It failed in fuel delivery and compression. I replaced the fuel pump&filter, intake and exhaust valves, and had a great shop rebuild the top end. It still would not start, and the spark plug was dry. I replaced the fuel injector and the plug was still dry. I tested ALL of the sensors/electronics with my fluke and all were within factory limits, yet I still cannot get it to start. It will kick over for a few revs if I shoot starting fluid into the throttle body, so the timing and compression should be good. I set the timing back to stock with the GYTR tuner. A Yamaha tech told me that the cam sprocket might have moved since it is a pressed fitting onto the lobe shaft, but I wouldn't think that it would turn over with starting fluid if that was true. I just want to get back on the trails and leave my friends in the dust. Any ideas or knowledge would be appreciated. 

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You say it failed in fuel delivery and compression and say you fix all but the fuel delivery and your plug comes out dry. I would think your problem solely lies with fuel delivery at this point. 

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2 hours ago, Bloody Knuckles said:

Hey yall. My 2011 YZ450F won't start. The original issue was that the timing chain skipped after a weird backfire during a ride when I tried to kick start it after a cool down. The tensioner was probably the cause although I don't know why since it only had 20 hours of use from the factory. I replaced the chain, rebuilt the tensioner, and replaced all the gaskets during the rebuild. Once it was back together it would not start, so I checked for spark, fuel, and compression. Spark was good. It failed in fuel delivery and compression. I replaced the fuel pump&filter, intake and exhaust valves, and had a great shop rebuild the top end. It still would not start, and the spark plug was dry. I replaced the fuel injector and the plug was still dry. I tested ALL of the sensors/electronics with my fluke and all were within factory limits, yet I still cannot get it to start. It will kick over for a few revs if I shoot starting fluid into the throttle body, so the timing and compression should be good. I set the timing back to stock with the GYTR tuner. A Yamaha tech told me that the cam sprocket might have moved since it is a pressed fitting onto the lobe shaft, but I wouldn't think that it would turn over with starting fluid if that was true. I just want to get back on the trails and leave my friends in the dust. Any ideas or knowledge would be appreciated. 

Is your valve lash ok?

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Just now, NAHA56 said:

Is your valve lash ok?

Dry spark plug would suggest a fuel delivery issue as well??

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Did you remove the fuel pump from the tank at all? Why I say this is because I had the same sounding problem. When I was reassembling the fuel filter and pump after cleaning it I didn't seat the pump correctly and this caused it to leak fuel pressure inside the tank and it wouldn't have enough to push through the injector.

 

 

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Toa84: Thanks for the insight. What was your original issue on your bike? How did you figure out the fault? PSI to the injector? I replaced the pump and filter with an upgraded aftermarket as I tried to hunt down the issue which requires disassembling the plastic pump basket. Did you bike run well afterwards?

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Did you remove the fuel pump from the tank at all? Why I say this is because I had the same sounding problem. When I was reassembling the fuel filter and pump after cleaning it I didn't seat the pump correctly and this caused it to leak fuel pressure inside the tank and it wouldn't have enough to push through the injector.
 
 

Toa84: Thanks for the insight. What was your original issue on your bike? How did you figure out the fault? PSI to the injector? I replaced the pump and filter with an upgraded aftermarket as I tried to hunt down the issue which requires disassembling the plastic pump basket. Did you bike run well afterwards?


Sent from my LGMS210 using ThumperTalk mobile app

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Toa84: Thanks for the insight. What was your original issue on your bike? How did you figure out the fault? PSI to the injector? I replaced the pump and filter with an upgraded aftermarket as I tried to hunt down the issue which requires disassembling the plastic pump basket. Did you bike run well afterwards?


Sent from my LGMS210 using ThumperTalk mobile app

My original issue was it wouldn't start at all. It would start if a squirited fuel down the throttle body but died as soon as I stopped. So I knew it was a fuel delivery problem.

I disconnected the fuel line from the injector and put a gauge in the end of the line (the gauge below fitted snug in the end) I then disconnected the electrical connector from the tank/pump and connect a 12v battery to it to get the pump running. Mine only showed around 10psi so I knew it was the pump. The gauge should show a constant 46psi.

After I sorted the issue with the fuel pump not seated in the basket properly it ran perfectly for 40hrs and then I sold it when I upgraded to a 2017. 91e473925e08a057cc0f4b9a70e9478e.jpg

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