Death on sudden opening of throttle

[Tony Bryant]

I've finally rebuilt my intake system (welded up from steel exhaust 
tubing), but I've got the following problem:

When the throttle is mashed at lowish RPMs i.e. <2000RPM
the engine dies for about 1/2 - 1 second, before getting its
act together and then pulling strongly. 

Sounds like not enough throttle enrichment you say... Not so, 
I've tried enough enrichment to sink a battle ship, and no
noticeable difference (just get lots of black smoke). I've tried 
from no enrichment, way upto pegging the injectors at 16ms per 
injector per cycle (100% VE requires only about 7ms)

My setup has a second set of injectors mounted on the runners,
if I switch to use these a the primaries the problem gets much 
worse. This indicates to me its something like fuel dropping out 
of suspension.

Changing the injection timing (Sequential system) does help a little, 
but not much.

FYI: I've got a reasonably small cam in it : 255deg @ .006", 40 deg 
overlap.

FYI: I sample the revs & MAP sensors 16 times a second, so its not an 
ECU response problem.

Q. Whats happening here? Theories anyone?

Q. Do other people here have this problem? Whats the solution?

Cheers.