there is more often than not a problem inside a carbureator, typically, those problems are water sitting in the carbs rusting up stuff, needle and seat valves that are stuck shut, diaphrams that are stiff old and hard, sometimes vulcanized ( glued ) to the diaphram cover plates so they can barely move inward to open the needle valves when necessary, or just partially open the needle valve which reduces fuel flow, gasoline/oil varnished internal carb parts, clogged internal filters, bad fuel pump diaphrams, ect.ect.ect.
Then to add to the list, water in the bottom of the gas tank, or a gooey mess of hardened pre-mix oil that seperated from the gasoline, a clogged up fuel selector valve, rotten fuel lines.
Bills86e