Been there, buddy. Except my misfortune cost around 600 after spendng 800. This time you start it for the first time. He should be paying for his mistake. Be sure there is slack in the throttle cable. Be sure that the slide is going "Whack" closed, and definately start it on the ground with the brakes pumped up. (Sometimes it takes a pump or two, after a bike sits for a length of time), and be ready. You can bind up the brakes and put it in gear to kill it. It could be bad on transmission parts, but you are only going to need it in an emergency. The rings start heating up and cause your fire, if you feed it air, it will run.
When mine did that, I pushed the kill switch, (nothing happened) pulled my tether kill switch for hillclimbing, (nothing happened) pulled the spark plug boot (still nothing) and then pulled the fuel line, then it died after a few seconds of screaming painful death. Panic was an understatement. It was such a Dumb@** attack, I am embarrassed to share. hitting the gas would have been better than pulling off the line. I started it up around a bunch of new cars, so putting it in gear seamed impossible at the time, but would have worked. Anytime you have a big air leak, hung up throttle or run out of fuel, it will rev uncontrollably, and you have to kill it with the transmission.
Be patient Wicked500, the nausea will go away eventually. I used the junk piston for a shop ashtray. How many $800 conversation peices do you have?