TOPIC:

I just bought a 1979 650c I am going to build into a cafe racer. I would like to run without a battery for minimalist appearance and I’m tired of buying batteries for 10 motorcycles. I would like to wire in a plug for remote start electric so I can use the electric starter when it’s cold in my garage then kick it over when I am out on the road. Can you leave a battery out of this electrical system? Thanks for any insight.

In general, battery is needed, not only to crank the bike, but also as base line or cushion for steady voltage at minumum RPM, when the Alternator may be not be spinning out enough to sustain ignition.

......try it,.......... disconnect the battery when idling and you'll see.
 

Bare bones for mattylight topic by loudhvx. 
Some of the diagrams are designated Batteryless. a capacitor is used in place of the battery & a size may be in the topic somewhere.
Here's page 24 from the topic with a wiring diagram for a 79 KZ650B.  you'll need to figure out whether or not it's appropriate for your 650C.
kzrider.com/forum/4-electrical/172746-19...mattylight?start=276

Over the years, Kawasaki used three fairly different charging systems in the 650s. You really need to know which one you have in order to make a decision. Lou, God rest his soul, could have answered the question in his sleep with one eye tied behind his back. Currently, we have a couple of members with extraordinary electrical knowledge, who should be able to steer you down the right path.

Edit as double posted for some reason 

Depends which model and charging system you have. Earlier models kick out 13+ volts at tick over maxing out out at 14.5 assuming your regulator is good. So yes it should run fine but add lights and any other drain you have and it'll be  borderline.
Assuming your thinking kickstarting it it? 
If so remember the coils will not be charged until the motor is turning over and at kick start revolution speed I think you'll have very little chance of generating a de ent spark to actually fire the bike up. 
650's in particular really don't fair well with low coil voltage even when a battery is fitted which is why they always benefit from the wired George relay direct battery to coil and kill switch bypass mod. 

Thanks for everyone’s expertise. I will see if it will run when I disconnect the battery and maybe run a smaller battery so I at least have spark when I kick start.

I am late to the party but these are my thoughts

• As Warren said, given that you charge charging system output at @2000rpm I would be surprised if the generator will give enough output to generate a spark at @200rpm unless you can pump the kick start like a steam engine 
  
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• I would advise against taking the battery out of circuit with the bike running, the charging system is controlled by battery voltage and also it is designed to produce more output than this bike uses when running. This additional output charges the battery. The battery acts like a "damper" in the electrical system (this is the purpose of the capacitor in Lou's model) without the battery to absorb the excess output there is a significant risk that you will fry the generator (stator, reg/rec etc)
• I would advise the use of a "small" lithium battery with a "MOSFET" reg/rec (specific for your charging set up) and "kick start" only as a small battery can't supply the current requirement of the starter motor 

You need a battery unless possible modification can be done to limit volts. Once on my 1978 kz650 I was riding along and for some reason one terminal broke off the battery. I didn't notice, and the motorcycle ran just fine, however I noticed quickly every single bulb was burned out. Headlight, tail, turn signals ect. Any bulb lit while the battery was "disconnected" was burned out, about 15 bulbs. Apparently the regulator/rectifier can not regulate voltage without a battery as a load.