1984 zn750ltd shaft drive

Hi I have a 84 zn 750 ltd
I just changed the motor with another good used one
I checked my compression in my old motor and 2 cylydres were realy bad
The reason I checked the compression was because it was realy hard to start cold ( no vacum to carbs)
So now after cleaning the carbs realy good and replacing the motor , it runs like a charme and fast idle cold and hot ( just like a new bike all over again ) but as soon as I start taking off it has no power at all but at idle it's the very best
I tryed another set of carbs that I had here and the power wow good power with the gas tank off so I though problem over but when I whent for a test drive I only made it about half a mile and it died on me , wouldn't start , so I put the petcock and prime for about 10 seconds and then it fired up again but just made it home and stopped again and even looked like not to much fire comming out of spark plugs , after I let it sit for about 5 minutes it started right up again
I even changed the pick up coil but the same

only 1 thing when I went for a drive I only hade the main gas pipe from the tank to the carbs hooked up because with bot lines hooked up it didn't want to run good at all

anybody got any suggestions pleaseeeeeee

Sounds like the battery might be weak and discharging to the point where too much draw by the battery is cutting the spark power (had a brand new glass mat battery do that to me and the bike would act like running out of fuel) but the issue seems to be fuel supply more to me, going to have to verify flow from the petcock and that the tank cap is venting, look for crud blocking the petcock. If you can use a test tank and high rev the engine (not WOT) for several seconds then the petcock/vent/crud is the issue.

Since you said plenty of power from the engine when in the shop it opens a lot of what it could be on the road, best to do things systematically rather than jumping from thing to thing, verify fuel from the tank first is flowing correctly then move on to the electrical stuff.