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Almost done rebuilding a 77 KZ750 twin, bike has 17K miles on it and has been sitting since '85. I've noticed the battery drains really fast (less than 15 mins) when the ignition is on, but engine off. The electrical system is currently only the ignition and charging, no lights or accessories are connected. When the ignition is on, I measure 4.5-5A being drawn, 0A draw when ignition is off. I'm using a 14AH lithium ion battery. When the engine is running, I measure between 12.5v (1000rpm) and 13.3v (~6000rpm) at the battery, so it seems like the charging system is working as it should. Is almost a 5A draw normal for just the ignition system? If not, 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.

Thanks,
Joe
 

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OK, for the sake of comparision, went to a Honda Fit, and this is a car with a computer drawing current even when off,....I used a DC clamp ammeter at the battery ground terminal....\

I measured, 0.46 amps with all off, and 5.4 amps when car is on ignition, but engine off. This is a car with big battery.

...then went to a '91 Kawasaki Zephyr 750-4, did same at the ground of the battery: I read 0 all off, and 0.77 amps with ignition on, engine not running, and no headlamp (have a switch for it).

I don't know how, or where, you are measuring the amps, but a draw of 5 amps for just ignition is way excessive for a motorcycle. Also, even though this is a old bike, 13.3 Volts seems rather low for a charging system,.....it should be at least 14VDC in my opinion. The '91 Zephyr puts out over 14 VDC, hitting even 15VDC sometimes, with the stock regulator/rectifier, (I have a permanent voltmeter on handlebars) but your bike is even older, so am not sure.


Yes, you would have to find what is drawing so much current, starting with removing what fuses you can, and then by removing light bulbs, or any connector you can, one at the time. .....then you may have an issue also with a degraded regulator/rectifier, or/and alternator......but correct the big draw first.
 

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….and adding to my previous post. You stated this draw is with no headlamp. Understand, a 55W headlamp if on, would draw 4.4 amps from 12.5VDC. ….forgot to mention, than also all my driving lights, including rear are very low draw LEDs.
 

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Thanks for the comparison info. Unfortunately I don't have a clamp meter, and instead am just using a multimeter inline on the battery ground connection. I'll start pulling pieces out of the circuit today to see if I can deduce what's causing the issue. I tested the regulator and rectifier using a multimeter per the service manual's suggested specs a while back, and everything seemed fine, but they're also 42 years old.

Does anyone have any suggestion on where to find replacement regulator and rectifier (they are separate units on the '77)? All I'm finding are the combined units that came on the 78+. Has anyone had luck replacing with a modern combo unit?

Thanks for all the suggestions, this forum is awesome!
 

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…...find the source of the draw first... I don't know if you have a problem with regulation, simply sounds low to me, but don't know with a bike this old, or whether is related to same problem. Fix one thing at the time. Don't discard either the possibility of damaged wire making bad contact to ground.

..I would also direct you to the KZrider.com forum, because it is truly a forum for very old Kawasaki's, including the KZ750 twin. Consequently there are many people there with a lot of experience, having done modifications or repairs, forced by the age of theirs bikes.
 

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Thanks for the comparison info. Unfortunately I don't have a clamp meter, and instead am just using a multimeter inline on the battery ground connection.
Most clamp on ammeters are for AC measurements, not DC. There are however some DC ammeters that you can hold up to a wire to measure current. The one I have has 2 ranges for starter and lower currents.
 
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