I Thought Vapor Lock Was An Ancient Phenomenon

You have a fuel flow problem, if your bike has vacuum operated fuel tap system start with vacuum lines off inlet manifold ! Or it is a filter blockage ! Try draining fuel float bowls if nothing else found may be water or dirt in float bowls ?

 

@capt is right ....... If you have water in the tank and its getting into the carbs that will cause the problem I would find a length of hose and drain the tank into a bucket and check for water there too.

It may be worth cleaning out the tank too if there is much dirt in there ( you may need to remove the tap to drain it all out )

If water has gotten into the external filter it will slow down the fuel flow through the filter too.

 

What about the filler cap on the petrol tank, is the breather hole clear, sounds like you get fuel for a bit when you take the cap off therefore venting the tank but when it’s been running for a bit drawing fuel it creates a vacuum starving it of fuel.

 

Yup water is a good possible culprit, and it can happen after one refill ! If you find water in any area of the fuel system it will take careful cleaning to remove it all, once cleaned out a little methylated spirits will help clean out any water that isn't visible , as it is hygroscopic it combines with water and will help any vestigial water to flow through and burn harmlessly !

 

Pick up coil or ignition coil sounds most likely culprit. The very fine wires break in the windings and go open circuit when hot. You can usually but not infallibly test the resistance value .....

Pick up coil (small 2 wire multiplug behind LH side cover adjacent battery) about 570 ohms. Main coil under fuel tank at front about 18k ohms between the HT sockets.

 

You'll find many happy to help and most suggestions are helpful or informative. Glad you got it sorted out in reasonable time