My bike had a similar problem, but I noticed that after I opened the petrol cap (to see if I had run out of fuel), and closed it again, the bike would start.
The problem was the fuel tank breather was blocked, so a slight vacuum would build up in the tank after about 10 to 15 minutes riding (depending on how full the tank was) and this would stop petrol flowing into the carbies.
Just try opening and closing the petrol cap next time it stops.
Or, of course, just blow back through the breather to check it flows air into the tank reasonably easily.

It could easily be some other problem, but it would be nice to rule this one out.
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[color=#808080][size=9]Yes,.. I too know how to waste Time and Money,...