Purring for months - today biting the dust

My '74 KZ400, love of my life, is suddenly terribly ill. She isn't accelerating properly - especially on inclines ( in a low gear) rpms drop and she stalls. Even flat or downhill, throttle being super inconsistent and weird. I was BARELY able to make my way home - she kept dying, total nightmare. I use only premium gas (only couple weeks old at most) - live in southern Cali, ride most every day, when i bought bike about 2 years ago had 1970s Japanese bikes specialist go over EVERYTHING. Surely this must be a minor issue, no? I'm going to change plugs, check wires, etc. Battery almost dead - I'm kick starting it every time for last couple months (15 year old niece has cancer, living 4 hours away temporarily and didn't have key.) The only thing I noticed is the left cylinder was not nearly as hot as the right - could it be that it's not firing properly due to jets/carbs or am I a complete idiot? (Yep new at this but trying to learn damn it!) I really appreciate the quick and kind responses from everyone on this forum  - you guys are amazing!

First thing you need is a battery. If it's drawing too much power everything else will suffer. It can burn out the stator, ruin coils and contribute to bulbs burning out. With a fresh battery you can trouble shoot anything else that is wrong. 

How are the valve clearances?

Some good suggestions so far.  Do you have points for ignition?  If so, they may be worn out.

I second replacing the battery.  My KZ1000 runs like shit when the battery is not in a good state.

And after changing the battery, check charging voltage by putting a volt meter across the battery terminals, and reving the engine to 5000 rpm.  Voltage should be in the range of 14 volts DC.

Nessism wrote:

And after changing the battery, check charging voltage by putting a volt meter across the battery terminals, and reving the engine to 5000 rpm.  Voltage should be in the range of 14 volts DC.

When doing this test it's best to apply load on the system (switch on headlamp high beam, turn signals etc)

Agree with suggestions regarding charging system. If stock it has an excited field system which does require  a healthy and fully charged battery to work correctly.