Real Puzzler on My 78 KZ650B

After sitting for years, a winter of work put it back on the road. Thanks for all help given here. BT46 tires are awesome!

NOW

If the bike sits a few days, I put the key in, push the starter and NOTHING. Lights are strong. Battery is new. When I went through the bike I checked the grounds and they seemed fine.

After pushing the start button ten or seven hundred times the bike will start right up. Turn it off, it restarts fine right away. Let it sit an hour and guess what same thing.

Battery cables are tight and solid.

Keys are original but it does it with both keys ...

Any ideas?

TIA

Could be the switch is making intermittent contact. I would open up the switch, look for a failed or failing solder connection. If they are good, I would spray the switch with some dedicated electrical contact cleaner like Deoxit. Do not use WD40 or brake cleaner or Raid.

Could be a loose connector somewhere in the circuit. I suspect Wookie58 or F64 will be along to provide an accurate and methodical test procedure to determine if there is a connection problem and where it is likely to be.

I'll suggest check ignition switch. I'm working on a KZ750 that sat for a long time. Got a battery and wanted to see if it would turn starter with plug wires pulled. Lights were OK but nothing when I hit starter. I tried De-oxit spray in the ignition keyhole but it didn't help. You could give that a try.

On the wiring diagram, there's a blocky drawing of the ignition switch. I used that to just ohm out the wires that run through the switch. Found the yellow to brown had no connection when the key was turned on. That goes to neutral switch so think that was the problem. Starter won't go if the neutral signal is not getting through. I ordered a new switch but just received it yesterday so not installed yet.

I had the switch gear off the handlebars because I pulled carbs. I was able verify the clutch switch and the start button were good before I opened headlight to get to ignition switch connector.

*To check the clutch switch, there were two barrel splices along the frame under about the middle of the gas tank (I had tank removed.) Two black wires I think. Just unplugged and checked continuity between them while pulling clutch lever. For starter button I was able to get meter leads onto the back of the push button.

It could be anything.

Do you have a magnetic compass?

Put a compass next to the starter solenoid.
Press the starter button.
Compass needle should swing towards the solenoid
The south part of the compass needle will be attracted to the solenoid

This will check to see if the starter solenoid electromagnet is being energized.

My '78 doesn't like to start sometimes using the electric starter button.
I know it's the starter button.
I have to press it, and wiggle the button in a circle.
She will then start.
I have bought a new push button with spring.
The starter and horn share the same part/button.
I just haven't gotten around to changing it.

Towards the end of the guide on the below link there is a flow chart for diagnosing a starter circuit by "Volt drop"

kzrider.com/forum/forum-index/faq-wiki/6...-fault-finding-guide

Don't know if OP ever figured this out, but my no start problem on KZ750 that sat for many years was ignition switch. I finally got around to plugging in the new switch and it cranks the starter now. Carbs are out so not ready to start yet but now starter turns engine (took off points cover and could see crankshaft was turning). With old ignition switch got nothing when trying to start, not even a click.