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. 

It's possible you have more than one problem. Electrical/battery as per the advice above, plus something else.

2 problems caused very similar poor running symptoms on my 440 (which is very similar to your bike). First one was catastrophic engine failure which required a rebuild. One cylinder running got it home. The other one was the points going out of adjustment and retarding themselves (screws not properly tightened on the timing plate) which was (happily) an easy fix. The symptoms in both cases were fairly similar: sputtering, noisy, lack of power. 

As this problem happened recently and it was working fine before, something has gone wrong. I would suggest, before replacing stuff (it gets expensive and you might not nail the problem) test everything you've got, and start with the easy things, like the contact breaker ignition. Check the gap, check the firing point is correct, and test the condenser with a multimeter (when the points go, it's often because the condenser has gone bad). It isn't always possible to see pitting deterioration on the points, but a bad condenser with blue sparks all over the place will take out your points. Then go and test your HT leads, your spark plugs, etc. If you don't find anything then start it up, let it run and squirt water at both exhaust headers. It should evaporate immediately from both. If you think it's running on one cylinder, then test that theory and it will narrow down the problem.

Battery is only a couple months old - but yes, I absolutely need to charge it - I think I brought the correct key down south to my brother's house 

Hehe. So I'm pretty sure I took care of the problem - embarrassingly enough, I immediately and frantically posted to the forum (and called two mechanics, and went by a motorcycle garage) before I did ANYTHING. Took a tiny test drive on our private road just to see how she's running, but was wearing flip flops/no helmet (stupid. I know.) Ahem. Changed the spark plugs, checked the fuel line, wiring, etc. Put in fresh gas - that was it. What a dork. I promise to run through the basics in future BEFORE freaking out and posting (and yes I will absolutely charge my battery.) On that note - if I don't have the key to open under the seat, can I pop it open with a screwdriver or do I need to call a locksmith? AAA? And yes, I'm a girl, but I'm trying, dudes!

No worries. I bet most of us are guilty of letting our imagination run away with us now and then.

The ignition key should operate all of the locks on the bike, unless somebody changed one of them.