So, you are riding 40 miles a week, at say, 30 calories per mile for moderate riding, you are burning 1200 extra calories per week. It takes 3500 calorie deficit to lose a pound, so your 1-2 lbs in the four weeks is about right. At this stage, this is why restricting food is so important.
For weight loss, I want to exercise 500 calories per day (3/4 to an hour of exercise) and I want an eating deficit of another 500 calories. That 1,000 calorie a day deficit will cause a two pound per week weight loss.
If I were you, I'd push up my intensity a bit on the ride (do you wear a heart rate monitor? If not get one) and keep your heart rate in the appropriate aerobic zone, and extend your ride to an hour and then monitor your calories as best you can. You will lose rate.
Good luck.
Bob