Assuming you have a carb and standard fuel tank, an in-line filter typically sits between the cylinders and heats up and can cause vapor lock. Check and clean you in tank petcock screen.
Just my opinion, based on having to troubleshoot this on my bike many years ago. I could go 60 all day long but at 65 it would run the bowl dry. If you stopped to check it out, it would flow enough to fill the bowl before you could check it. Fuel filter vapor lock was the issue.
I have been using a Russell inline filter for a couple of years with no ptoblems.
I was just very carfull where I put it so as to be sure it would be exposed to much heat. It's not clear but it comes apart very easy for inspection