another starting problem

I have a 1978 chevrolet motorhome with 350 and quadrajet. If you let it sit for more than two days it will not start without starting fluid. It will crank and crank until battery is about dead. Put starting fluid in it and it fires up and runs perfect. It does this if is hot or cold outside, summer or winter. I tried taking the carb off and had someone epoxy a valve inside as they thought it was the float bowl leaking into the intake, made no difference. If you only let it sit for one day it will fire right up. I thought maybe a fuel pump, but once it is running, it runs great at all speeds. Any ideas????

Sounds like a pin hole in the fuel line letting air in and draining the fuel line back into the gas tank.

I had an aftermarket in line fuel filter with a bad seal. It only got damp with gas when running. It would go a week and then the engine would have to be cranked for a long time before it regained prime.
....something to check for anyway...

the pickup in the tank could be bent which could cause the tank to become vapor locked

Welcome to AF. These carbs are famous for the float bowl plugs leaking this requires removing the carb base to access the plugs for resealing.