The juice comes from the solenoid, if I remember.
But if you have your fuel pump still original, it may just be too old and
the brushes only touch when it's cold.  You may not even able to drive it
too long without it stopping the car.
One way I found it out once, I let the car run until it stopped, and then
tried to run the fuel pump directly from the battery and then it would not
anymore.  But I waited for twenty minutes and it would run for an other
twenty.
The warming up can also mean, that the connector on the solenoid as it
warmed up has gotten bigger and it got a little more loose.  Electrons are
physical objects, and if they can't jump over fast enough an masse, your
thingy won't get powered up, I guess.
Zoltan

-----Original Message-----
From: john
Sent: Wednesday, August 05, 2015 6:34 PM
To: vanagon@GERRY.VANAGON.COM
Subject: No ignition on restart after 5 to 10 mile drive in 90+F weather

A gremlin from the past seems to have reappeared on my '84
Vanagon (1.9L) engine.  It started the other day after I
went to move my van after bringing my Son home from high
school (10-mile round trip plus plenty of waiting time in
traffic at high school).

Engine turns over fine, but does not fire.  Possible smell
on unburnt fuel.  The tach need flutters a bit while starter
is engaged.  After leaving van to cool down for a few
minutes or longer, it starts and runs fine.

My first suspicion is that there is dirt on the contacts in
the big connector between the fuel injector cable and the
fuel electronic control unit, and that I should clean the
contacts on both sides of the connector with CRC-626.  This
was a problem many years ago, but only showed up in cool
damp weather.

My second suspicion is that their is a problem with the
ignition control unit.  I replaced that unit in 2003 when I
put in a Boston Bob long block.  The fuel injection cable
and the fuel ECU are the same ones that were on the van when
I bought it in 1997.

I would appreciate the wisdom of the list in solving this
problem.

John