OK, so I went for a spin this afternoon, been a few months since I last rode it. It was a bit lumpy when I set off, ran on one for a bit (not for long) but then it seemed to clear up. Happily pulled through the rev range for an hour or so then when I pulled in for a quick break, clutch in and it died, no tick over. Then it didn't start. It turned over with the odd huge backfire through the exhaust. AA turned up, nice fat spark but plugs appeared to be dry. A squirt of easy start resulted in another huge backfire and a call to get it recovered. It has fuel, I can hear the fuel pump running so where do I start looking???