10 yz450f random power chop -- with Video

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  • ScottYo

Posted September 15, 2014 - 07:57 AM


I've been fighting this issue for the last 2 years...


Randomly the bike will just surge/ chop / loose power for a CH


here is the video evidence... 



at 0:06 - you can hear it very distinctly

at 0:14 - you can hear it AND see the font end dip



At first it seemed only to happen in 5th gear, but that was a red herring, it does it in all gears. 


GYTR tuner = no codes


Ive worked with the lead mechanic at 2 Yamaha dealers.


It was on a dyno and hooked up to a FI Diagnostics tool, but did not exhibit any errors or do the surging.


have replaced...


fuel pump

spark plug



wire and boot from coil


gas cap

clutch, plates and basket

tested stator (its okay and in the range)

tested crank / flywheel pickup (its okay and in the range)


have also rebuild the whole motor...

new cam chain, tension-er, valves, cut seats, piston, crank via crankworks, transmission parts - worn (red herring) 4th and 5th gears, whole enchilada




The only thing else is... ECU, airbox sensor, H2O sensor???



Any Ideas? -- Your help is greatly appreciated!

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