318 timing

No way would I run less than 10* initial timing. Unless you have to go through emissions testing, throw the book numbers in the trash where they belong.

It takes time, effort and work to get the timing profile correct. Stock distributors usually don't allow for adequate initial timing.

Simple test. Start the car and have it idling, give distributor a smidge of a twist to advance timing. If the engine picked up RPM, it wants the timing. PERIOD!!!

Let the engine tell you where it wants the timing.

You may also have some issues with fuel evaporation. It could be boiling off and flooding the engine. Really bad issue with todays fuels in non-sealed systems.