more boost help please

[cush]

ok today i have taken my car apart again to get to the bottom of my boost issues.
 
My problem is when i accelerate i have no boost and it doesnt cut in until about 4000 revs then it cuts in and all works fine until i let the revs drop down again and no boost again i have seen there are 2 valves bolted to the upper inlet manifold and one is the 3rd one along on the bottom of the rats nest which control the boost if i am correct?. I have checked them all and they all work fine
 
What makes the boost cut in??
 
any help please as it is doing my head in now not been able to boost properly for 4 months