This morning I fired the bike up to head into work and when I got to the top of my driveway (lucky) it ran out of petrol. No worries just switched to reserve and headed to the closest servo.... an independent. The ride there was problem free and I filled the tank with 95.... I always run 95. Anyways after I switched the fuel valve and got on my way I immediately noticed it running rough at low revs, kinda like it was running on less than 4 cylinders, this continued for the 20mins trip into work and when I arrived and switched the bike off I noticed a strong scent of petrol but I could see no leak. I switched the valve off and went about my day. Seven hours later I fired the bike back up for the return journey and noticed it was running fine........ for about 5 mins....... then it started running rough again same as before. Runs like its missing from a standing start but smooth about 3000rpm onwards. Again once I arrived home I inspected for any leaks but could see none.... both with engine running and not. Does anyone have any ideas on possible causes? It had a new fuel valve installed about 500km ago, the spark plugs are about 750km old. I put some fuel treatment in it this evening, will see what happens in the morning. The bike in question is a 1996 CBR900RR.... carbureted, manual choke etc.