Blowing Black Smoke even after tuning carb'

[Stephen Moss]

Started blowing black smoke last week, Blowing gas out exhaust. Low power on a 350 with Edlebrock 750. Tuned carb but still doing it on accelaration. 86 GMC 3500. Could it be fouled plugs? New cap and rotor and new wires and plugs 6 months ago. Low miles. Any tips?

 

[rich weyand]

What plugs are you running?

How did you tune the carb?

 

[scottybaccus]

May be a stuck float, or debris in the needle & seat. Edelbrock carbs are sensitive to fuel pressure, so anything messing with the float will result in flooding.

 

[firebane]

750cfm? Do you have more than a stock engine? I'm going to say that carb is sitll running pig rich.

 

[rich weyand]

750cfm? Do you have more than a stock engine? I'm going to say that carb is sitll running pig rich.

Agreed. Do you know what jets and rods are in it? Was it a new stock carb when you put it on? Did you adjust the float height? The Edelbrock float heights are always wrong new right out of the box.

 

[MadOgre]

Valve seals?

Rich jetting can cause power loss and excessively rich could cause black gasoline smelling exhaust.

 

[MadOgre]

If you have a 750 cfm Edelbrock square bore carb with the original jets and rods on a 350, guaranteed the jetting is rich. Way rich!