Go to the level area of ground at the peak of Mt. Chiliad, where the mountain bike race is located. Take out a rocket launcher. Aim at the Mountain Bike. The green reticule will home in on the bike. Fire at the bike and blow it up. Then, aim at the bike again, manually. The second time around, the reticule will not automatically aim on the "wreckage" of the bike. When you fire a second missile at the bike, CJ will catch fire. You can be 30 feet away and still catch fire. Also, the same effect has occurs when firing a missile at the bike to "blow it up", then shooting it with a sniper rifle. However when using the rifle it will usually require two or three rounds before CJ catches on fire.