Today, I set off on my 1998 250 Burg (genuine 6000 miles on the clock) for the first ride out since the middle of December. I let the engine idle for about 5 mins before setting off (clear weather, crisp 6C - 43F). Straight away, very poor acceleration and wouldn't pull above 35/40mph. I ran the bike on the centre stand and it revved easily up to max but as soon as it was under load again it was back to 35mph, tops. So, after letting it run at full revs for about 2 mins on the stand I tried it under load again and that seemed to fix it. Until, after about 70 miles and close to home the Burg suddenly decclerated from 70mph down to 40 mph again and absolutely no guts on any incline (by now it was steady rain)....anyone any ideas??