It seems like a fuel problem, unless you have faulty new ignition components. You should check for a good spark, however, immediately when the bike starts to die on you--carry a spark plug in your pocket and check for spark on the side of the street. You should also make sure to keep your battery charged while you sort this out. It will be draining at idle, and eventually a low battery could cause you some trouble too.
Also, try reading a plug to help you decide if you've got too much or too little fuel. Clean the plugs before you head out on a test run, and when it sputters, pull em both and see if they look lean (white) or rich (black)
While it does sound like a bad diaphragm, I find it odd that it would rev up when cold but then start to die when warm.
If you went through the carbs right before this problem started, I would make sure that the enrichener discs are not backwards If they are, the bike will run way too rich when up to temp.
AfromNH's suggestion is a good one. Check the fuel flow at each carburetor by removing the bowl and opening up the fuel tap. There is a specified fuel amount that should flow out of each carb. You can probably find it on this website or Snowbum's I can't recall if the carb vents through the small brass standpipe or elsewhere, but you need to make sure that the carbs and the tank are venting. While you are checking for spark on the side of the road, you could also pop off the carb bowls and check their levels. Make yourself a dipstick to keep things quick and easy.
