Had a problem with my bike recently. I pull on the choke and thumb it, comes to life, first crank of the starter. Even if been standing for a week. Leave the choke full on for about 15 secs and can then close it, to about half way for a further 30 secs and can then close it fully. Bike will continue to run without any problems. Put bike into gear and then pull away, change into second gear and open throttle, bike coughs and splutters and almost stalls until close throttle and reopen. Then no problems through any gears or for rest of ride. At first thought it was because engine wasn't warm enough but I did try warming the bike for 5 minutes before riding off. Still happens on that first gear change and first real opening of the throttle. Anyone any ideas?