Spyder 1980/starting problems

[Réal Forest <forest-bousquet@domain.elided>]

This is my first submission. So I ask for mercy if I mess it up...
I have a 1980 Spyder with the original Spica pump. Here is the problem.
When the car is cold, I have no problem starting the car. When it's hot-
say after a 100 mile drive, and I stop the engine, I cannot restart it,
(except of course by getting someone to lend me a hand pushing the
car...)The starter will not crank the engine: my mechanic - an
experienced alfa mechanic- changed the ignition switch. A brand new one.
It apparently did not entirely cure the problem since I had the same
mishap today. We checked the wiring: it's ok. We checked the starter:
it  will crank the engine if one connects directly the positive and
negative on the starter.
Has anyone any idea about the source of the problem? Actually  the car
may be very hot- say if I drive in town for quite a while- and using the
ignition switch,the starter will crank the engine without any problem.
It's only if I drive for a certain time- like an hour- that the problem
happens.
I would appreciate any bit of help.
R. Forest
Montreal, Qc

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