I have a 1985 k100 I press the starter button and it turned over for a few seconds then stops turning over, you can press the start button again and it will turn over again but after 3 srconds stops turing over (it won't continue spinning the starter)
I can repeat this over and over it acts like it will start. It actually started last week I rode it about a mile and it died and then did as before turned over but not starting. It has new gas, new plugs, new battery. Any ideas?

Check the wire connectors under the tank. Mine did similar for a while when I first got it. It had loose wires everywhere.

Have you pulled the starter and checked the brushes?

Are the guts of your ignition switch clean?