use the pitfall trap and set it right underneath the kut ku while its stunned. THEN plant the large barrel bombs next to the trapped kut ku.
Set off the Large Barrel Bombs with Small Barrel Bombs and the damage will deal twice as much while its trapped, leaving you with extra time to set the last bomb or combine more and set them.
Lg Barrel Bomb: Gunpowder + Large Barrel
Gunpowder: Fire Herb + Nitroshroom
Sm Barrel Bomb: Fire Herb + Sm Barrel
Oh, and if you think you can do it, stick with the Hunter's Knife and keep going to the Hunter's Dagger, and eventually to Assassin's Dagger. I suggest doing the ore paths because most bone paths aren't available because you need med monster bones, lrg monster bones, etc... which you can't get at the time. the ores you CAN get, so just keep mining those Earth Crystals from Forest and Hills until you get the Assassin's Dagger. Trust me, you WON'T regret it. That thing'll take you through the Quest Level 3 Star missions like nothing, and even the 4 star quests. change weapons after that before trying the 5 star urgent quest.