1990 mazda b 2200 blows smoke from exaust when first start
Black exhaust is typically unburned fuel. If the ambient temp is very cold, the fuel enrichment system (choke on carburetor - longer injection or activation of "fifth injector" on fuel injected engines) will allow extra fuel into combustion chambers to facilitate cold starts. The fact that the black exhaust quits in a short time is a good indicator that at least part of the fuel delivery is correct. (Typicaly, carburated engines are a little less responsive than injected engines and over enriching was fairly typical at cold temperatures and this is one of the biggest reasons that car manufacturers went to better control with injection). I also do not believe your CTS is defective since an open default is about -45F, and you'd never see the black smoke go away as the engine would think it was always that cold. Mazda has aways been somewhat problematic with fuel control issues ever since I was a neophyte mechanic, and if the vehicle runs well once you get a little heat in it, then I'd not worry too much at this time.
What do your plugs look like? If they are black and sooty after the car has been run fully warmed up then you have a problem. A little black smoke when cold is probably not a big deal if your gas mileage is good and you are not getting gas in the engine oil.
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