Pump a little of his gas into a container, toss it on the ground, and drop a match into it. I've seen gas go so stale it won't match-light in a month or less, and if he's gotten some Diesel fuel onboard, it definitely won't start!
If the plugs have gotten fuel-soaked, it's possible they have a conductive path down the porcelain, no matter how new they are. Edit: I re-read your original post, and I guess I missed seeing you'd already done a plug swap. If they're fuel-soaked again, at least heat them up with a torch. It's possible the carb is flooding so badly it's soaking the plugs at every starting attempt.
Just an observation- - - -Demon carb, headers, Accel ignition, high-dollar wires, and probably a lot of other go-fast stuff just isn't necessary for street use. It sounds like somebody is more interested in bragging about all the expensive accessories the engine has than actually building in reliability. I spent a lot of years building NASCAR race engines, and I didn't use half that stuff to win races pretty consistently. My engines ran 7K RPM + on stock-appearing parts and easily outran most of my competitors.
Jerry
