I have a 1989 Honda Accord Dx Coupe with 72,000 miles on it and it blows a black smoke from exhaust when you first start up the car in morning? Also you have to keep your foot on gas pedal for first few minutes otherwise it might stall and you get a smell of gas coming into car also? What could be causing this? The car has a carburetor also. Also mileage has dropped from 26 mpg around town to 17 to 18 mpg?