Fuel pouring out of the sight plug is a symptom of a float that is adjusted too high or alternatively as mentioned a sunk float. In addition, the fuel dripping after shut off is a symnptom of too high a fuel level in the bowls.

On our 70 RR with a 383 and a Holley 950 vacuum secondary carb it used to act as if it were running out of fuel at the track, when we were doing 1/8th mile. I finally did the obvious, checked the floats, and they were too low. Fixed it and the problem went away and the car will go full throttle to the 1/4 (finally got back to the 1/4). The running out of fuel symptom just showed up as before the car ran fine, so the float levels can change on their own.n It also said to em that they are pretty sensitive to float levels as it was not many flats on the adjusting nut I had to turn.

A check for a sunk float is when you have the carby apart is to take the float and shake it. If you can hear liquid sloshing, the float is leaking.

Good luck!