Weird fuel pressure mystery!!! Flow stops. '90 Kawa. Vulcan motorcycle.?

Here's a problem I've never been able to figure out. I have a transparent fuel filter on my petcock which then splits to the front and rear carb fuel lines. Everytime I hop on the hwy (75-80mph) to work I notice the level in the fuel filter drop slowly. By the time I get off the hwy the bike's sputtering, the filter's empty. I have to pull over, remove the filter, let fuel pour freely from the tank into the filter to fill it and then plug it back onto the petcock. Then I'm set for another 10 minutes or so. Sometimes it empties again, & sometimes not. The weird thing is that it never does it @ night on the way home. In fact, I drove back one night from Daytona to Orlando & the bike was fine. At 1st I thought it was pressure-lock but I tried riding with the gas cap off and it still does it. When the filter empties (with gas cap on or off!) you can see NO gas dripping from the tank. As soon as I pull off the filter the fuel pours out freely from the petcock. Very weird! Any ideas?

I THINK I GOT IT!!!!! Well, I drove to AND from work today and no problems!!!! Here's what I did.

First, I replaced the round spring-clamp on the filter hose with a screw-type clamp. It's a much tighter seal now.

Second, I removed the vacuum line from the filter housing and re-routed it up and back under the tank pointing towards the rear. I read on this forum about someone who was having some vacuum problems rerouting his hose like this and it fixed it.

All in all, I think it was a vacuum line problem because while testing, when the filter was half-empty and wouldn't fill I sucked on the hose to see what happened and immediately I heard like a bubbling sound and fuel flowed into the filter and filled it up in a second. Also, I read on line that these vacuum hoses are better off pointing up as to prevent vacuum lock. Maybe that's what was my problem. Anyway, great ride home, thanks to all you guys' suggestions. Thanks a million!

You have a "small" air leak past a slide or diaphram in one or both of your carbs that is causing just enough pressure in your fuel line to prevent fuel from flowing into it a gravity feed system it dont take much

clogged vent hose on the carbs
see those small clear plastic hoses hanging off the bottom of the carbs?
get an air compressor and blow some air thru them, they are clogged
if that don't work then your problem is low engine compression