TT600R won't start(but once we tow it, it runs perfect)

[wonky]

One of our TT600R's has decided it doesn't like starting. It got progressively worse over about a week until now we can't start it with the kickstarter at all and have to tow it, then bump it in 3rd gear. Once we get it going it runs as usual, although he has to leave the choke on for a little longer than usual. When its hot, ie within 10-15 mins of stopping it will kickstart.
Theres an intermitent medium pitched knocking noise its started doing as well. I'm not sure if its a valve or something nastier. The knock is in time with the rpm.
I'm thinking the starting problem might be a blocked pilot jet but haven't stripped the carbs yet
Any other ideas from the wisemen?
Cheers