Hard-starting '91 200Q (only when cold)

[Barton Oleksy]

Not sure if my mechanic has checked the fuel-pump check valve - could
that make it hard to start (turns over for 5+ seconds) when the car's
been sitting for a while?  There's a cloud of smoke out of the exhaust
once it does start, and a very gassy smell in the vicinity for a few
seconds.  Car also runs rough for the first couple of blocks, then is
great after than (aside from some lifter-ticking noise).  Thanks for
your advice/suggestions.

Bart