Hey spanky. Are you using a "heart rate monitor" when you ride? If not, get one!
To get the most out of the ride, you MUST keep your heart rate in the Aerobic range to insure you are getting the most benefit from your riding. I am not expert so won't even attempt to recommend a range for you. I use the numbers provided by my doctor. 140-165. I try to keep in the mid 150bpm on a typical ride.
I have also lost over 100#s and am now in within 50#s of my goal. It really is much harder to get the inches to come off. I'm now in 38" pants. Lost 7#s and still in the same size pants. There is a lot of places you can loose fat/weight. The tummy is only one of many. Keep cranking and good luck.