Hello there, newbie with a problem here. I've had my SV650S ('99) for a few months and it's been good as gold up 'til now. I had covered about 85 miles of my 88 mile journey tonight (fortunately!), pulled away from the lights in first, second, third, all okay, then into fourth and she lost almost all power. I juddered my way home, backfiring when the throttle closed. Thought it might be icing, but I waited an hour or so for the carbs to warm up and it's as bad as ever. Idle is fine, but then struggles as soon as the throttle is opened

. Any ideas veterans? I'm stumped.