My CB500 let me down this morning. Started OK, rode about 500 yards before it just ground to a halt - no power, and as soon as I stopped it stalled. Cranked it for ages, it fires very slightly with choke but not enough to run. It's a brand new fully charged battery, serviced a couple of hundred miles back, and yes - there is petrol in it. Any advice on what might be up? I'd really like to get to work tomorrow on it. Thanks