I just had my 455 rebuilt about 3 mouths ago and the stock motor only .30 over other than that bone stock. Car has not left my shop other than in the back yard ( no miles I was starting it weekly sometimes just to let it run. then it started running really ruff SO first thing I did was pulled a few plugs. Plugs looked ok but had a little black film on them put 8 new plugs in and still running a little ruff on top of a little black smoke. But motor cranks every time but a little ruff after new plugs so I talk to my engine builder he said carbuerator is louding up due to the ethanol in gas and not being driving. Do I need to replace the carbuerator or put a rebuilt kit on it oh yeah it is a edelbrock 650 carb I would like to have a qjet but I am worried about clearance. Oh I forgot to mention after tuneup I played with the ajusting screw on front of the carb still no success. I am clueless.

 

I tend to agree with your mechanic about the fuel! Todays gas attracts moisture. Put some fresh fuel and sta-bil in it and see what happens.

 

I disagree, ethanol makes it run leaner not richer.

Sounds like you may have carb issues nonetheless. I'd rebuild it, double check your fuel pressure and float level and go from there.

 

if it has an aftermarket fuel pump even stock replacements sometimes pump out more than the stock psi if your fuel pump is pumping out more than 5.5 psi that could be it but also i agree with cutlassfi check your settings i bought an edelbrock carb that had NO FUEL FLOATS man was i mad i had to take a part new carb

 

Check for sticking float / needle & seat.

- Eric