Standard 1.6 air box assembly causing restriction

My standard 1.6 escort has always bogged down when I use close to full throttle. I tried a bunch of things the other day and realised it ran perfectly with no airbox assembly however when I install it the car doesnt want to accelerate properlye. I even ran it without the filter thinking that was the issue and that didnt work.
 
Anybody have any ideas as to why it wont run properly with the standard setup? Anybody had this issue before?
 
Engine is bog standard, just rebuilt along with standard rebuilt carb. All standard emmisions gear hooked up with no leaks in that department. The car had the issue before the rebuild too so hasnt just come about all of a sudden.
 
Dont think I have any vacuum leaks around the carb as the engine dies straight away when I cover the carb
 
Any help/advice/opinions would be greatly appreciated as I am running with the top cover spaced up to make an opening around the top of the airbox to make it work and look standard at the same time.
 
Cheers,
Ryan

Cheers martymexico
 
Thats what i reckon Ill have to end up doing. Just cant figure out why a bog standard motor wouldnt work with the standard assembly. Not only gutless but really struggles to rev with it installed
 
Cheers
Ryan

Yea youre not wrong troppo, has me very confused to say the least!

I did have a bit of a play with that. It didnt seem to be working all that well  but with no vacuum (i blocked the line off) to it the flap stayed in the downward position so that meant the air would go straight in the front of the intake with less restriction than if it came in from the bottom and had to turn a corner.
 
Cheers for the idea, might have another play with that part. Will put a photo of what ive dont to rectify the issue soon and a photo of that part you mentioned phoenix 13918
 
Cheers,
Ryan