Backfiring when starting

[Shiny]

Hi all,

Every now and again my 05 EC300 backfires a 'chuff' sound out of the pipe when kicking it over, normally when giving it a bit too much gas. I'm thinking it's timing related and have had a small mess around with it before. I've elongated the hole in the locking tab on the stator and advanced the timing slightly (roughly 1mm of rotation), this seemed to give me a little more top end but hasn't got rid of this anomoly.

Compared to other 2 strokes I've ridden, it refuses to start when given a wristful of throttle, preferring to be started like a 4 stroke with little to no gas. It idles and runs perfectly so I don't think it's down to jetting, which is set to the recommended UK spec anyway - #7 slide, N1EF needle on 3rd clip, 40 pilot and 180 main. Plug always looks fine on removal.

Should I give it a whirl trying it retarded from stock?

Thanks.