I have a 80 vette with edelbrock preformer intake and a 1805 thunder 650 cfm series carb.  My car has a small cam. headers, no cat. My car is running rich. Is the 650cfm to much for the car? black soot in the tail pipe and it seems like im getting 6 miles to the gallon. I have a chance to buy a edelbrock 1806 for 140.00 only 300  miles on it. What should I do? The car seems to run great no back fire will maybe a slight miss from what I was told.

The 650cfm shouldn't be too much for the car. Might just need the float levels set. A "slight miss" might be a symptom of running rich, too. I'd have the carb checked out to see if there is a problem with it.
A weak spark from the ignition system could also create this issue. Have you checked the plugs to see what they look like? When was the last time the engine was tuned up(plugs/wires/cap/rotor etc)?

well I had new plugs and the car tuned up by pros but never realy got to drive it because I so many other issues to work on with the car. Now Im at a point where I can drive it and it is running rich and burns a lot of gas. If a 650 is not to much I guess I will buy the carb for sale. My concern was that the 650 was to much for the car and it was putting in more fuel then the car can handle. When I first push carb from under the hood it drips gas just a little then sprays. The new carb has a electric choke what do I hook the positive wire to?

I have the same intake combo on my 80.  I get about 12 mpg and 16 hiway.  The car runs great and its the perfect carb..

do you have auto choke or automatic? guess I will buy carb hope this fix the problem its cheaper then having this one rebuilt

I have the automatic - I should have said I have an 81, not an 80....  Essentially the same being the computer and smog is all removed. It cost me 150.00 to have my Qjet rebuilt so 140.00 for a new carb aint bad..

IF the car has been sitting for a while, while you do other things to get it road-worthy, it's possible there is some doo-doo in the carb, even tho it was clean when you installed it originally. Could even have something in the needle & seat that is causing it to flood a little.
Definitely sounds like you have a carb issue. Replacing it may cure it, but it might only be a minor issue that could be fixed quickly, and painlessly, too.

A agree with Joel, the other problem is the replacement carb. You say it only has 300 miles on the carb, but has it been sitting for quite some time as well? How can you be sure it won't have the same issues as the one you have now? A good rebuild and flow test by a pro can really help, and the replacement may need the same thing as the one you have. These carbs are pretty simple, and almost bullet proof. I think I would go for the rebuild, myself. You might end up with two that don't work right.

ha ha ha listen to this. When I bought the first carb I was not for sure how old it was.

There ya go!