Oldsmobile/Buick Repair: cranks with fuel and spark but no start, neutral safety switch, voltage readings

Question
1990 geo tracker 4x4 will start when cool but when run for awhile will not start. But will start when pushed, and compression started as it being a manual. Is it the neutral safety switch or the starter?

Answer
A starter or neutral switch won't even let it crank over if that is what you are saying....but a loose wire, bad ign switch, or several other things will act the same way.
Making sure it is in neutral, I would start at the starter, jumping the solenoid, and see if it cranks then.
Some voltage readings would be useful also.
Van