Vacuum problems

Hi ive an 86 vf500 interceptor and having fuel flow problems. May sound a mad question but i recently checked the petcock and the rubber O ring was totally screwed. Would this being faulty cause the fuel to not flow to carbs,as there cant be any vacuum if its leaking? I know this may seem a mad question but just trying to eliminate problems as i try to give the bike a makeover

I think you’ve got it in one

Tnx for reply Biff