Can anyone shed any light on the following?

Suddenly my XT is taking ages to start. You crank it over and over and eventually, when the battery is nearly dead, it will start but has to be revved to keep it going. However, no matter what you do, it will die again and then takes a couple minutes of prodding again before it restarts.

I've changed the battery and spark plug which was before this fault ocurred. Even with a fully charged battery it does the same every day. However once it is warmed up, it will happily restart every time until left for a few hours.

Any ideas?

Thanks in advance.