Brian,
There's a good chance you should use less lit coals to start. It depends on the quantity of meat in your smoker also. The meat will act as a heat sink as well. What were you cooking, what was your target temp and how many lit coals did you use? My general method is to select the quantity of lit coals based on the quantity of meat in my smoker and the temp I want to maintain. Less lit coals for lower temps. I always put the meat on right after dumping in the lit coals. I then monitor the temp on the way up..
Doing it this way makes it much easier to maintain the desired temp; it's too hard to bring temps down. I start closing vents 40-25 from my target temp. For some cooks I'll only light 10 briquettes and for others it may be 20.
Paul