I had the same problem with my GPW during refurbishment we changed the coil to a new one, the jeep ran like a clock, hot and cold but was very difficult to restart once hot, I tried timing, carb, valve clearances. air leaks etc. I thought it was maybe fuel vaporisation and lived with it for a while. Last winter I decided to get it sorted once and for all I thought back to all we changed during the refurbishment and remembered the coil so I dug the original out and refitted it and hey presto the jeep runs perfectly I even realised it runs better at all temperatures than it did with the new coil fitted. Just because an items new doesn't mean it's ok same goes for condensers there are many faulty batches out there.