TOPIC:

Almost done rebuilding a 77 KZ750 twin, bike has 17K miles on it and has been sitting since '85. I noticed the battery drains really fast (less than 15 mins) when the ignition is on, but engine not running. The electrical system is currently only the ignition and charging, no lights or accessories are connected. When the key is on, but ignition switch set to the off position, I measure a 2.5A draw, and when ignition switch set to run, I measure 4.5-5A being drawn. There is a 0A draw when key is in off position. Also, if I disconnect the regulator from the system it goes down to 0A draw. I'm using a 14AH lithium ion battery, and I'm measuring the amps via a multimeter in-line with the ground connection. As for charging, I measure between 12.5v (1000rpm) and 13.3v (~6000rpm) at the battery, which seems low. Is almost a 5A draw normal for just the ignition system? Any suggestions for troubleshooting where the draw is coming from? It seems like something isn't right because I would think I should be able to have the ignition on for longer than 15 mins without a completely drained battery. As far as replacing the regulator, all I'm able to find are the combo reg/rec units that came on the 78+. Can you use one of the modern combo units, or do I need to find separate units?

Thanks,
Joe

I guess I'd check to see if the ignition system is draining the battery. As for the charging system, loudhvx probably has a good explanation somewhere here on KZR of what the 750B has. You can check the diagrams at Kawasaki.com or Partzilla to see what you have. The 77 750-B2 diagrams show two different generators & two voltage regulators. Your motorcycle probably has a single phase stator, but I don't know that much about it.

Simplified wiring diagrams. KZR topic >> bare bones for mattylight by loudhvx >> Pg 11
some of the diagrams are no longer there (pgs. 1-10). But from pg. 11-on many are still available.
Maybe one of his diagrams might help to figure out the charging system n stuff.
...

I could be wrong but think your system is 3 phase excited field system. This field will be energized once the keyed switch is turned on. But it will only generate power to the battery once the engine is spinning. The system makes use of separate regulator and rectifier. The regulator provides power to the field depending upon a sense wire that is connected to the entire electrical system.

It is my understanding that the newer combo units (reg/rect) will not work with the system.

(As gd4now mentioned) when the bike is not running, kill switch off, but ignition switch on, the regulator will draw full power through the field coil (rather than regulating it). That could be about 2.5 , just like you measured. (No other lights etc.)

Your ignition coil should measure about 4 ohms. That means if the engine is not running, and the points are closed, the coil will be drawing somewhere around 3 amps, and that should drop a bit as battery voltage lowers and coil resistance increases with heat.

So if your ignition is truly drawing 5 amps, you should measure the primary resistance of the coil. (That's the small wires.)

I must be missing something here. Why would one have the ignition on, but engine not running for 15 minutes? Ed