Does anyone have experience of making a conscious effort to adapt and how long did it take before you for back to carb fuelled levels of performance but with a lower heart rate?
I've done fasted riding - so longer slower rides without breakfast - start taking on carbs 45 mins into the ride. I've also done it with shorter higher intensity rides on an off-road commute.
It didn't help me lose weight but it did radically improve my endurance.
your body will use carbs as a priority over anything else
At higher intensities. At lower, it'll prefer fats. See this graph:
Where the graph starts to go up, that's where the rider starts getting energy from carbs. Below that it's fat (although a small amount of glycogen is used when metabolising fat iirc).
Zone 2 training is enough to move this upward curve to the right, but I suspect it's more effective when riding fasted also. People who tend to be sprinters like to sprint, so naturally their graph has a short flat section, which is why we like to take on carbs and then use them, and then take on more etc. Sounds like the OP is a sprinter. Endurance based athletes (slow twitch, lots of Type I muscle) naturally burn more fat so end up thinner and like doing long rides, but can't sprint so well.
I'm aware this will mean I become slower in the meantime to get faster in the long run.
Doesn't quite work like that IME. You'll always be slower fasted than you will well-fed. Your fasted performance will improve, but when you then ride with lots of carbs you'll find your well-fuelled performace will also have improved.