[Vwdiesel] IP acting strange, new symptoms

[Val Christian]

A month or two ago I wrote about my 91 NA Jetta, and how it will
sometimes "hang up" and not fuel above idle.  A twiddle of the foot 
pedal, between idle and some higher power setting resolves the 
"hang up" every time. 

The injectors were new 5000 miles ago.  The cylinder head was reinstalled
about that time.

The "hang up" problem, which seems to occur when shifting, more
on left turns than straight ahead, and almost never on right turns.

A new development...now the car smokes.  Soot out the rear pipe...not 
clouds, but more of it than ever before.  The injectors are new, the fuel 
is clean and flowing.  The fuel screw is factory set (never turned it on 
this IP).  I still have to investigate, so I can't say that there aren't 
air filter obstructions, or anything else.  But I can say that the power 
is OK, and in the ball park.

Oh, and in the most recent tank, I added an injector "cleaner" additive
in low quantities (per manufacturer).  I don't think that four new 
(factory rebuilt) injectors have all failed at once, though.

So before I go digging, would anyone like to offer their suggestions
as to what I should be looking for?   Thanks.

Val