1993 Civic running rich

Hi I have a '93 civic with a b16a2
vtec (out of a 1999 si) anyway I had
the car about 4 months now and only
driven 20km a month. Yes (twenty
km) anyway.. Recently as soon as I
start the car I can smell gas in the tail
pipe, at idle it is medium grey, and
when I rev it it spits out dark
grey/black smoke. It happens when
the car is warm or cold so it can't be
the cat or oxygen sensors.. Also im
in canada and it's below 0 celcius.! it
seems like this started happending
as winter came around.. Maybe just
a coincidence. Anyway thanks for
any ideas as to what can cause this
rich running. Thanks a lot. P.s. I
recently mig welded a patch next to
my 02 sensor so could that have
screwed it up? But as I said its rich
when car is cold too. Ok thanks a lot.