Rebuilt bike runaway throttle

I finished rebuilding 1980 KZ550A and when I tried starting it the engine took off and went to max revs 9000 so I shut it off. The throttle control was off and the cable had a bit of slack deaccelerator cable was normal so I tried starting it again and same result went to max revs. I can't figure out what is causing it to take off? During the rebuild I took the carbs apart cleaned all the gunk out cleaned main and pilot jets. I was only able to check and remove one of four main jet needles as the screws holding the slide arm to the throttle shaft were seized but the one I did remove was clean and looked okay. When I turn the handle bar control the cables move the throttle shaft normally.
Any suggestions would be appreciated, I struggled to get the carbs on between the air box boots and the manifold ports and I don't look forward to taking the carbs off to re-check them but I don't have any other ideas.
Thanks Tomas

I changed a throttle cable once and had the same thing happen when in my haste I forgot to tighten the clamps on the carb boots. A good air leak will do that. Drive the revs right up.

I forgot to follow up. The problem was one of the inner carb boots was not sealing and I didn't spot it and the vacuum line was not sealed properly.
I have gotten better at taking the carbs off and re-installing them. One of the keys is to warm the air box/carb ducts with a hair dryer. I take the guts out of the air box, put the hair dryer in the air box and turn it on. Then I disconnect the throttle cables, the gas and vacuum line, drain the carbs, loosen the carb boot clamps, then roll the springs back on the air ducts, and when the ducts are soft then I roll the duct lip back off the carb carefully so I don't damage them. The carbs can then be pulled out of the boots and taken out. Reverse the process to install the carbs.