Trouble Starting My 1977 Fiat 1800 Spider

[Lon]

I have a 1977 Spider 1800
After the engine has been running for say 1/2 of an hour, and I turn it off and try to restart the engine, I need to wait for about 20 Minutes before it will start.
I have had this problem since I bought the car about 4 years ago.
I have replaced the timing belt.
Bypassed the fuel pump by adding an electrical fuel pump
Insulated the fuel line from the firewall to the carburetor
Added an additional switch, which continues to run the radiator fan ( temperature gauge stays below 190 )
Added a new fuel line filter.

Can you offer a suggestion

Lon (mpi@mailtime.com

[So Cal Mark]

sure, several suggestions;
make sure the engine is cranking at the correct speed. Worn starters can cause slow cranking.
Make sure the engine is getting spark
Make sure the fuel isn't boiling in the carb, effectively flooding the carb