retarded maf?

[Wei240]

i know this problem is similar to many others, but i'm not quite sure what's wrong wince it was running fine for several months...

if it's not one thing, it's another,...

just when i was about to do a compression/leakdown test this weekend, it appears that my maf decided to crap out (yet to be determined..)

here's the scenario:
- difficult cranking/turn over (if it turns over):
- bad idle
- spews black smoke
- engine shake and shimmy like crazy

car/mod:
- redtop
- walbro
- fmic
- 3' piping
- safc

what i've done so far:
- malfunction code = 12, so it says maf...
- made me a cheapo boost pressure/leak tester (which i did find and fix one leak)
- changed new spark plugs and gap to .28
- went to junkyard and got 2 mafs (89-90 sohc)
- started the car with maf and unplugged the maf, no difference, sputters and black smoke

so, i might have bummed out and got 2 defective mafs, but, how could i test if maf is truly faulty?
tested the 3 wires that connects to the maf, one is ground, the other has battery voltage and the other current is very small when the key is on the ignition

could this be a symptom of something else?

it was running fine for several months prior...