It is cutting the green wire that goes to the cdi. It gives the bike an extra 1,000rpm up top. Do a search for some pictrues or description as to the exact wire.
These hondas come lean from factory. He prolly rejets it too. If there is no new filter on your friends bike, my money is on some better jetting and the wire mod. Dude prolly makes like 50 bucks if that's the case.
TRX450R...Pulse Charger, 12.25 HH, HotCam S2, KW valves and springs, P&P, UNI filter, airbox outterwears, Woodward fuel screw, Denton stabilizer,ProArmor K/S, Elka Elite longtravel 17" w/dual linkage, Figair airbrushed hood, Holeshot fronts, Razr II's rears, AC Propeg nerfs, +1 1/2 stem, Armidillo skids.
And a very well modded 03 warrior, engine, suspension, etc