I weigh right under 150, and I do my wheelies in 2nd and 3rd, kinda pulling back on the bars moving my weight, and one leg back on the grab bar, knee on the seat, and right leg ready to slam the rear brake on.
I suggest try 1st, pull your weight back and just gas it. Should be able to get up a little. Do it on dry grass or grippy dirt, not loose, and it should lift fine. You could start in 2nd also if you want. 1st revs out way to quick for me, thats why I use 2nd or 3rd for wheelies. Like he said above, make sure rear brake works and be ready for it, if you plan on riding the wheelies very far back.