I think yer talkin about some entirely different setup Pete, there's no return line on these ol trucks, nor is there any 'pressure' in the carb, the "check valve" [needle and seat] is controlled by the float and prevents the bowl from over filling - and if there's a properly functioning fuel pump and gas in the tank, there won't be any air in the line when running
the problem with Rochesters is simply that they're leakers from new, and the bowl is vented to the atmosphere, allowing evaporation
Bill
