A few other things to try also, spark plugs - very obvious but often overlooked, and while you are in there it's perfect time to do a compression test. Bit more involved after that is valve clearances, don't know if you have had them checked at the service interval (around 16k) but if not they could be too tight, compression test results should give a hint if they are. If you are lucky, it could just be bad fuel or a fouled up plug, those iridium tips don't like to churn on the starter too much before firing up, hopefully it is the easier of options. I was very unlucky a couple of years ago and had a damaged valve that got worse gradually, sputtering at junctions but okay on the open road, valve had slight deformation at the valve seat, had to take the head off and replace the valve but I doubt very much you will have an issue like that, my bike is generally ridden hard so it does have a hard time but oil and filter is changed every 1000 miles road riding (a lot less if doing any tracks) and it never gets thrashed until up to temperature.
