1979 KZ400 - Weak Spark

I'm having issues with my 1979 KZ400. The problems started at the end of last summer when the bike became harder and harder to start. Cut to this year and I can't get it to start at all. I replaced the spark plugs which got the bike to start and I was able to take a 15 minute ride, but once I shut it down it would not start up again. I've been working through the ignition troubleshooting in the Clymer manual, but I'm hitting a wall. I've replaced the battery, coil, spark caps, plugs, and condenser. The spark is now very weak and intermittent.

Voltage at the battery is 12.3 volts, voltage at the points is 11 volts. Is this pointing to some electrical gremlin stealing juice from the ignition circuit? What are the troubleshooting steps at this point? The fact that the spark degraded (bike got harder to start) over about 10 separate times times starting seems to point to some component that would fail in that way. I'm new to motorcycle maintenance, so what that could be I don't know.

Any help is much appreciated.

Has the bike been started and running since you put it away for the season after last summer? Did you put Sta-Bil or something similar in the fuel tank and run the bike long enough for that mixture to get into the carbs? Did you drain the fuel bowls before storing it for the winter?

I'm not saying your issue isn't spark, but specifically why are you convinced it is the spark?

What's the voltage at the coils with just the ignition on?

ajsfirehawk, thanks for the response! I did put a stabilizer in the tank and ran the bike before putting it up for the season. I did not drain the fuel bowls. I'm leaning towards an electrical problem because I've watched the spark get weaker from the time of replacing the plugs until now. I suppose there could be some gunk in the carbs that could cause some rough running, but the one time I did get it started this spring it seemed to run smoothly, and normally. If the fuel/air mixture was off, could that screw up the plugs enough to result in weak/intermittent park? (the bike did start up right away when I put the new plugs in)

What's the voltage at the coils with just the ignition on?

MoveOver - Voltage at coil is 9.9v

Should be 12 volts. Check of you have 12 volts after the keyed ignition switch.
Most of the time it will be the on/off switch on the right handle bar. Clean all of
your electrical connections.


.

If cleaning all your connectors doesn't help, go through and ensure all your grounds are good and feel along the harness as best you can to look for possible breaks.

If it persists, you may want to pull the wiring harness and unwrap it to go through thoroughly. It couldn't hurt to give it a good deep clean and inspection. Afterwards, re-wrap it with the non-adhesive self sticking wire tape.

All good ideas; this tech article from my website might help:
wgcarbs.com/index.php/using-joomla/exten...-categories/89-coils

Honestly, this sounds like compression is low. When was the last time the valves had clearances adjusted or compression was checked?

Thanks for all the responses guys. I've been working away on it, cleaning electrical connections and checking voltages all over the place. I found that when I pulled the headlight off, I'm getting almost near battery voltage at the points. I'm just at a loss, as I'm getting power to the coil, and I've tested the points according to the manual which says they're performing as expected. I ordered a new set of points since that's the last part of the ignition circuit that isn't new, and it's a cheap way to rule that last piece out. It has gone from a weak/intermittent spark to no spark at all.