85 GPZ550 Power Loss

Good afternoon,

85 GPZ550, starts, runs, idles great. Carbs were just rebuilt with factory settings (I think). Around 7,500 to 8,000rpm. The bike just falls right flat on its face. Pulls great right up until that point. Bike got sent back to the shop (hopefully I will be the shop one day). I couldn’t quite get a solid explanation but the mechanic states if you aren’t full throttle, it will buzz right up to the red line. He had a friend who ran a Kawi dealership take it out and he isn’t sure what is going on either. 
The carbs have 116 jets (or around this as I can’t recall) and he is going to try 124’s as they both believe it’s a fuelling issue and not electrical. 
The bike has a new battery, unknown make of aftermarket 4-1 exhaust, stock airbox and paper filter, new spark plugs. 
Anything that would cause the bike to just die out at high rpm? Could it be electrical? 

Thank you all!

 

Heard back from the mechanic. The larger jets work and the thing will zing right to the redline now. So, if you have a bike that you don’t know or maybe changed the exhaust on, then it falls flat up high, larger jets might be your answer.