....and it was burnt!

My first attempt at BBQ was a chicken on a rotiserrie using lump charcoal. I
had a difficult time keeping the temp regulated. It bounced between 225 and
325, according to the thermometer in the grill lid. I cooked the chicken (4
lbs) for 1 1/2 hours. The outside was charred black but the meat was still
relatively juicy and tasted good. I had noting on the chicken but some salt and
rubbed it a bit with some vegetable oil.What did I do wrong?