That shouldn’t be too much carb, it’s a bit large for a 305, sure, but I don’t see how that couldn’t be remedied with an Edelbrock tuning kit like this one:
Before all that though, go through the basics.
Check timing and make sure your fuel pressure isn’t above 5 psi on it. Install a regulator if need be.
Easy way to find a leak is to take the carb off and put it on a stand or bench vise, put a couple ounces of fuel in it and let it sit.
Now I’ll caution you, my carb was likely screwed up, as no carburetor should drain fuel out overnight with no airflow through it. So while I suspect it, it’s an unlikely culprit.
Go the tuning route first.