dude i reckon 300-350kms per tank(35L) is alright around town, i normally get 320 or so befor i fill up.
one time i filled up all the way until it poured out of the tank (about 1-2litres ended up on my car, i was day dreaming at the servo.) and i was coming home from canberra and done about 350kms on half a tank (freeway average speed of 115-120km/h doing about 3500-3700rpm) so i reckon its just the start stop thing that drinks up the fuel.
as for the black smoke ????? no idea and i dont see any from mine may be there is but i don't see it.
a question to the gurus out there... i have a problem with my car.. late 91 corolla GTi... the things is that after a fairly hard drive i park the car overnight and start it the next morning and when i start it a SHIT load of white smoke comes out (exhaust) for about 10secs...so whats wrong?? and theorys appreciated.