396 engine problem

[geezer#99]

So you have a stock bbc. Runs funny when hot (sometimes) and great when cold.
That tells you float is good.
Likely heat percolation.
THere's a couple cures.
A heat plate to isolate the carb from the hot intake. Like this.
http://67-72chevytrucks.com/vboard//...d.php?p=936440

Other thing to check is your initial timing. Retarded timing makes lots of heat.