put my other fzr 400 3en2 back together the other day and would not tick over or rev past 1k,
took the air box off and it revs as normal back on again and not reving
no blockages in aor box at all
what do i do run it with out one what can i use to stop crap getting in the carbs?

It could be it's running very rich and taking the airbox off is leaning it out enough to get it to rev. Checkyou have the choke cable on propperly and maybe clean the carbs and have a look that the slides aren't stuck ... are the plugs new ???

Have you checked that there are no fuel hoses squashed or trapped under the airbvox or tank?
Make sure the cable's & linkages' are clear too.

problem sorted was carbs rubbers they was shot replaced them and all is fine now