Bike won't run right

[Fawkesy]

Hi. Posting for my friend. 2000 I/s.
Bike will start right up when cold, run for 10 minutes (exactly each time) then start running rough.
Let bike cool for 10-15 mins, then try again and exactly at 10 minutes runs rough.
No vaccum leaks, no carb / fuel problems. Fresh gas. Checked all coils - okay.
Can anyone help us out?
Thanks so much.

[Mr.BubblesVRCCDS0008]

Pop the tank cap open and see if it stay running longer, maybe be the vent tube is plugged and pulling a vaccum on the tank.

[Fawkesy]

Thanks Mr.Bubbles.
Tried that...wasn't the issue.

We just tried the bike (with gas cap closed) for 35 minutes and she ran good!...now i'm really stumped.

[Gryphon Rider]

Sounds like it may be a tear in the vacuum diaphragm in the fuel valve.  The valve partly opens allowing fuel to flow at a reduced rate.  If the problem improves with a full tank of gas it strengthens my theory.  Higher fuel pressure pushing past the partly closed valve is better able to adequately feed the engine.