rm85 wont start after rebuild
 

hi i have a 2004 rm85l
i boiught it as a non runner, stripped it down, new crank,main bearings, seals, piston and ring, new stator,new plug, fresh fuel etc
now im no novice, ive rebuilt quite a few mx engines with no problems
now my problem is it just wont start, it has compression, good spark, fuel etc, carb float heights all good, and nice and clean inside,
any ideas? im baffled as this seems very strange