As others have said, in order to lose weight you have to set up a calorie deficit.
An average man, without taking excercise into account, should consume about 2,500kcal a day to stay at the same weight. A 500kcal reduction in intake will translate roughly to 1lb weight loss a week, but it will fluctuate. You don't really want to lose more than 1-2lb a week or you'll get ill. So you can either eat 500-1000kcal less, or do exercise amounting to 500-1000kcal, or ideally a combination.
It's worth bearing in mind that shorter rides more often will probably give you more consistent weight loss that longer rides infrequently. I cycle to work every day, but it's only 10k each way and takes me 30-40 mins. I reckon that's about 500-600kcal daily. I don't get to go on longer rides very often, only once or twice a month. Nevertheless I have lost 1.5st since the beginning of the year, which I'm happy with.
I am 6'3". I was 16st 11lb at the beginning of the year, and right now I'm 15st 3lb. I aim to be a whisker over 14st by the end of the year, and then maintain that.
I wouldn't worry about not seeing much weight loss after only a few weeks, it can take a month or two for it to become apparent.