Backfire

[Val]

Only happens on warm up? Does it only happen with the choke on?

Yes only on warm up when on choke only. I do twist a nudge of throttle when starting on choke. I know it is recomended not to use any throttle when on choke, but if I not use at least a little throttle the bike can't start.

If you've just changed the plugs it could have significantly changed the spark/fire characteristics, meaning you don't need as much choke angle/duration as you are used to.

I've recently changed my for the first time since owning the bike.  Before the change I needed choke on for a couple of miles before I could take it off and not stall.  With new plugs I can take it off after a couple of hundred yards.

Actually I have changed the plugs some time ago last year and it was working fine. The whole backfire started after the K&N filter.

I will buy soon OEM filter and will see what happens next  :lol