could my carbs use a rebuild?

ive finally gotten my bike to get spark (78 kz650b) but it has a real hard time starting. it sounds like it wants to start but wont quite. i have to litterally hold the start button down for about 10 seconds. once its run for about a minute, if i shut it off and turn it over again it fires right up. i would really like to be riding this summer. please help

Sounds like the choke is not working.

the choke does seem to have something to do to it. when i push choke lever down ( i think this is off?) it doesnt sound like it will start at all. but if i put it in the oposite position it half a little life, just barely though. just the sound coming from the exhaust sounds different like there is a little combustion or something. guess i need to know which position is on and off on the choke first

I'm pretty sure down is "off" on your bike, and it's easier on the bike, if you use the choke whenever the bike is cold.
If you could afford the rebuild kits, and think you can do it, I'd rebuild them. You can just try to clean them up really good, and reuse everything - just try to go easy on the old gaskets when tearing them down.

I've owned a lot of KZ650s and most are a bear to start if they have sat more than one day. The problem is aggravated further by fooling with the stock airbox, using pods ect. Further aggravation because electrics are barely up to the task to fire the plugs when the starter is turning. Low compression also takes its toll. My guess is rebuilding your carbs will not do much good. You probably have the usual combination of problems coupled with an engine that was never known to fire up with the first instant of push of the button. If you have a vaccum petcock sometimes it helps to turn the lever to prime when starting after sitting.

now i can start the bike 5 hours later and it still fires up. just sitting overnite its a pain on initial start up