Robin, this is one downside to a single ended fuel system (no return, regulated in the tank) is that there isnt constant fuel flow to help cool the rail (and keep cooler fuel flowing). I still think its a heat soak issue with the fuel.

Not related, I am back in Ginza now after two days testing in Sendai Japan. Just chillin' in the hotel overlooking a nice view of Ginza at midnight.

 

I'm going to put on my "old" hat here to recall my bought new '66 912 that developed the same problem after only a few years of ownership. Solved by adding the starter relay trick mentioned above. It was all related to heat soak contributing to high resistance. Suggest you run a test when it occurs by using a freon spray with an extension tube on the nozzle in the direction of the starter (NOT water!) to cool it down. If that allows it to start, then you have a starter going bad as mentioned above.

 

Chris, I am jealous, I would trade position with you any day of the week. I love Japan, especially Ginza.

NC TRACRAT - There are no starter issues as the cranking speed of the motor is the same cold or hot.