Poor Idle / Engine Dying

Hello Everyone,

I am a proud second owner (dad was first owner) of a 1977 KZ650 C1 and I am currently in the process of bringing it back to life. I am running into an issue and I am hoping someone can point me in the right direction to a fix. The problem I am experiencing: The bike will start no problem, idle poorly then die or die when I give it gas. I have found that when I start the bike and hold the brake in with the brake light illuminated, it will idle much better. I have also found that with the brake light on, the hazards on and the headlight on, the bike will idle MUCH better and I am able to open the throttle and it revs like it should. It seems that with the more power/volts the bike is drawing, the better it runs...
Do you have any suggestions as where I should start looking?
Just a few things that have been done: Carbs are clean, coils and plugs are new (gapped properly), points seem to be in good shape, fuses are good. I am happy to answer any questions, it may be easier than me listing everything else that has been replaced/updated. 

Thank you! 

Normally when strange things happen it is down to corrosion causing electrical resistance. Start by cleaning all the main earth points and see how you go. I can take you through some voltage checks once you have checked the basics.

Can you think of the last time it ran well and describe any changes to the bike since then?

When cleaning the ground (earth) connections, be sure to remove the screw so that both sides of the terminal and the surface it should connect to can be completely cleaned. Some 800 grit aluminum oxide paper will do the trick, but in most cases I prefer a dedicated electrical contact cleaner like Deoxit D5. It does a great job of removing most corrosion, and it leaves behind a light corrosion inhibitor that does not interfere with conductivity. Some people recommend dielectric grease, but I really dislike it for general use and only use it where a manufacturer recommends it.

Thank you for the responses, I am going to start with the ground/electrical connections first and let you know how it goes. As far as last time I heard it run correctly... probably never. When I got the bike, it was sitting for a REALLY long time in the family garage. I got the valves redone as the timing was off and they were bent. I went through cleaning the fuel system (tank, petcock, carbs). Carbs are clear of any/all debris. It may be running lean, so that is another area I will have to explore.