Oh, it will wheelie fine. I ran a monster Baron 4.60x18 knobby on the back of mine and it would plow a trench whenever I wanted. I love them - put 28,000 miles on my first one. When I ride a late model 250 - there is just day and night differences. You must show respect for the newer, water-cooled 250's and their near 50 horses.
They were probably the best on/off road bikes you could buy. I've got several scramblers and they are jokes. The DT series could handle some major mud, jump hills and terraces, plus had godd ground clearnce - all the while had turn signals, mirrors, and would ride 2-up. As said, I really enjoyed mine. I have a CL175 and an Avenger SS 350cc - neither one is anywhere near as capable as the little Yamaha off-road. The little Avenger will almost do battle with the new 250's power wise though. That little 350 makes 40+ horsepower as is a wheelie machine.