Mitsubishi L300 does not start!!

Dear Mitsubishi friends, I have a (small) problem with my Mitsubishi L300 (built in 1991, 90hp): Once it has reached operating temperature (after about 15 kilometers), I turn it off and want to start it again, it does not start. I have already renewed the battery, the distributor cap, the distributor fingers, the spark plugs, the ignition cables, the ignition coil and the Zünsschloss. I am at the end of my wisdom.