wierd engine noise

[lethalmethods]

I bought a 2001 400ex a few months ago for a great price. It ran good and strong. It has the 440big bore, stage 2 hot cam, air box opened, gutted the pipe and K&N air filter. Well I cranked it up and moved it to my back yard today and shut it off. When I cranked it back up it made a "slapping" sound and shut off. When I try to crank it over it makes this "slapping" sound in the motor.

I am wondering if anyone has any advice on what the issue is before I begin tearing it apart.

[sprayedgt]

I had almost the same noise with my brand new '08. I took it out 3 times and put just over 120 miles on it. The last time I rode it, it ran awesome. But later that night when I got home to put it in the garage it was making a "gurgling" and almost like an electric arc/slapping sound then it would shut off. It wouldn't rev too good either. Since I had the mileage on it I took it in and had the 1st service done and all seems well now. I guess it had something to do with the valves being way out of spec. I'm taking it out riding Saturday so I'll see if it runs good. If not back to the dealership with it:(