I have a 1992 Zenith Carburetor on a Ford LSG 423 (similar to the picture shown below). My question is that if the machine sits overnight or longer, there is a Viton tipped valve at the fuel inlet that gets stuck closed thus not allowing fuel to enter the carburetor and giving me a no start. I take it apart and reassemble and it starts and works for the day. Any ideas on what might be causing this? There is a tiny spring inside the Viton tipped valve also. Do I need to change this assembly out etc? The valve doesn't show any visible wear. Any thoughts?