Percolation is most likely.It will not only occur in the carburetor bowl but in the fuel trapped between the fuel pump discharge valve and the carburetor float valve.
When the engine is cut off and air flow from the fan ceases,this trapped fuel soaks up heat, expands possibly to boiling and the increase in pressure opens the float valve to raise the bowl level and spill down into the carb throat.
Some times you can get a indication of this by vapor/smoke issueing from the carb throat after this "heat soak" has commenced.or some times liquid fuel leaking from the throttle shaft.
some things that can help:
metal line instead of rubber
line routed to avoid hot areas
if an in line filter is here keep it installed low and as cool as possible
make sure the heat riser valve is free to open --I might even block it open
insulating spacer-as thick as possible between carb base and manifold
insulate fuel line from pump to carb
I'm not sure I've seen it on chevy but Pontiac and Olds in the 60's-70's had a small bleed off line either on fuel pump or filter that bled down the fuel trapped under pressure in this part of the fuel supply system.
And when all else fails-- the old cure for a "flooded" engine.Crank it with accelerator on the floor.
Aint this modern gasoline wonderful?
