Fuel delivery issue

I tend to agree unless the vacuum hose collapsed momentarily, otherwise the petcock was operating properly. . I went through the gas cap and didn't see any issues there but cleaned it anyway. I'm thinking it was some issue with the diaphragm or vacuum since it started almost immediately on Prime. Since I had a spare diaphragm I replaced it and also replaced the vacuum line with a really thick strong new one today. The fuel filter seems to be flowing freely, and I thought about an air block, but it would seem that would have also kept it from working on Prime. So I guess I'll just ride and if it happens again I'll try to isolate the issue on the road.

 

when i have air in the fuel line i set it to prime and the air goes into the tank, it will not go into the tank in on or res position with motor running. I would not expect it to go int tank in with motor off unless there was a petcock problem.
I use a transparent fuel line

 

I use clear fuel line also and I've always had some air in the fuel line as well as the filter. It's never been a problem, but I'll re-position the line and see if I can get the bubble to move into the tank at Prime. Thanks for the suggestion.