As far as carbs reducing endurance on the bike... it may be true for the most seasoned athletes (which I doubt are posting here in the Clydes/Athenas forum) but fat is an excellent source of energy for physical activities. By dropping your carb intake, you'll be converting your body into a fat burning machine instead of a carb burning machine. Your body will adjust over time and will be satisfied with fat as a fuel during exercise. Track your calories. If your going to be doing a long ride, go ahead and eat more calories (still low carb) but make sure your exercise still results in a calorie deficit if you want to lose weight.

If I'm going to ride hard, I want it to result in weight loss. I'm not going to set any speed records. I'm not going to race. I enjoy cycling but one of the side affects that I want to get from riding is fitness and weight loss... not performance and speed (I'm sure both will show improvement, but I don't have any goals in those areas.)