it started last year having rear cylinder issues. bike sits for a week and when i try to start it, it starts but only have hot exhaust front front cylinder. anywhere from a few seconds to a minute later the rear kicks in and runs fine. at first i thought it was a fuel issue. carbs were gone through while i had here inside, clean enough to eat off of. fuel delivery is there, no kinked lines ect. ect.
out of the blue it will drop the rear cylinder for a few seconds then fire back up. ive gone over the wiring harness, no breaks, no grounds.
could it be rear coil or ignition box? pick ups out of whack or am i off base and it is a fuel problem. other than maintenance this bike has been great and want to keep her running. i do have a spare bike for parts.
what do you guys think?

Did you check your float levels when you had the carbs apart?

What does the spark plug look like after this happens? If plug is wet and not fouled, it is most likely a spark issue.

What is the battery voltage when this happens?

My 750 did that from the word go, even after the carbs were disassembled and cleaned thoroughly. It always had spark but for whatever reason the back cab lost all or most of the fuel out of it after it ran for a very short time it would do just exactly like yours and straighten up and run fine.

Does it do it only on cold startup and run fine the rest of the day?
That's what mine did. I just let it idle till they were both firing and rode it.

Mine usually had to sit overnight or longer before it acted that way again . I said good enough and put about three seasons on it and sold it when I bought the Beast. I told the buyer about its odd little quirk and they rode it that way for a couple of years . I would see it on the road all the time after that.

Mine would also occasionally do it too

Mine is the same way. I just keep the choke on an extra five seconds, the back cyl. gets fuel, rpm rises, then I back the choke off a little.

Usually has to sit more than a day. Don't think it happens with daily riding.

at least im not the only one, its fine for a few days then it does it. i was getting ready to tear back into it when i posted. saved some down time. thanks guys