Sounds like idle circuits in the carb, to lean to keep running. If pushing the gas down a little while holding brake and it stays running that’s your problem, nothing electrical. If distributor is stock make sure it’s 10 degrees btdc in neutral, advance hose disconnected. One other thing to try, while running in neutral squirt carb cleaner around carb base gasket and edge of manifold. If the idle increased you got a vacumm leak. Carb could be so far out if adjustment it’s won’t idle correct. But do the other stuff first then to next test.