Outer Limits 4x4 Board

Ok.. So I have recently fitted an Airtec snorkel onto my Sierra..
And I have gone to connect the snorkel up to the air intake..
BUT.. I have discovered that the pipe that I am supposed to be connecting the snorkel up to.. Is sucking in little if not no air..
I have NO idea why!!
I pulled the air filter box off and checked for cracks etc. But none exist.. So I would like to know.. Why on earth the thing isn't sucking in air!

Is there a good seal around the top of the carby?

Yeah brand new!
I have checked the air flow all the way to the beginning of the air box.. But then it just seems to lose suction..

Does the engine run? are you just putting your hand over the intake trying to feel for suction? If the engine runs it's gotta be sucking air from somewhere

I know my old airbox didn't completely seal and there was a small hole in the bottom of it too.

If you can block the air pipe from the airbox entirely and the motor doesn't stall then you;ve got a vaccuum leak somewhere. If you've checked the carby to the airbox then it's possibly post carby. This could create other issues too.