Just taken my X out for a spin after not using it for 6 weeks due to a back problem. All good for a few miles then it just died on me. Managed to start it again after a few minutes but only got into third before dying again. I checked the plug and managed to limp home but it was spluttering and backfiring it went for 30 seconds then stalled but would restart and then do the same again. I fitted a Kev mod about 25 miles ago. Could this be the problem? It also smelled a bit hot when I got home. Any ideas?