Hard to start and back firing

My nephew has a 2011 YZ 450F bought as a left over last fall. Hasn't done anything but ride it and has had no problems until today back firing when he kicks it and hard to start. Is fuel injected of course. Any ideas?

Is it a brand new bike or used? If it is back firing that usually indicates a lean mixture or air leak in the exhaust. As far as hard starting this could also be due to a lean mixture. Did he get the GYTR tuner.

It could also be simply because the plug is fouled. We're talking starting problems here, not decel backfire on a carbed engine.

There is, with EFI, a number of things that can do this, and the first thing to check after the plug and verifying spark is whether you have fuel being delivered. You can remove the injector from the throttler body, or separate the TB from the head, whichever's easier, leave the electrical and fuel connections intact, and crank the engine to see if the injector squirts (mind the presence of sparks or flames). If not, get a tuner connected and see if there's a hard fault code set.

Thanks grayracer your 1st suggestion was it. New plug and it's running like a champ. Thanks again. :)

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