I've noticed on rare occasions when I'm on the highway at normal speed 65 and then to make a pass I'll step on it to aquick 75-80 and back off the gas to 65 or so, at the point of deceleration theres a small amount of smoke from the exaust 1-2 seconds or so. Never smokes at any other time, (start up etc). Could it be excess fuel from quick acceleration to deceleration? Kinda unnerving. Thanks

 

the general rule is black smoke - fuel .... gray smoke - oil ... white smoke - moisture vapor ... Sick

 

It is dark, so it probably is fuel, since no smoke at any other time. I didbuy a rebuilt carb, but have not really put it to thetest yet.

 

If you don't really "get on it" often, it can also be residue (carbon, etc.) built up in the exhaust system. Or too rich a fuel mixture can give you that. I liked the exhaust pipes on my '69 Z/28 to look grey/white as a sign that it was tuned/running properly (never black looking pipes), but that may be too lean a mixture for todays fuel.
Clyde

 

could be trany fluid from the modulator depending on vacum line routing
check the trany fluid , are the plugs clean, i mean if the modulator is bad it will pull trany dluid into the vacum line and burn it through the engine, sometimes fouling a plug ......posibly