Motorcycle Questions? Ask a Mechanic.
Hi and welcome to JustAnswer, I’m Louie. Sorry you had to wait awhile but I’ll do my best to help.Initially and to avoid asking you to do something you've already tried, can you please tell me what / any and all troubleshooting / specific steps you've already attempted other than the above; "...Rebuilt carbs changed fuel lines..."?
Is the described symptom of "...idles fine but bogs down@4500 rpms ..." present even before the carbs were rebuilt?
Have you checked the spark plug burn color?
...test battery voltage when idling? ...and when attempting to rev?
Appreciate the additional information.
Still and on:
And is the air box + filter installed? ...fitted correctly/tightly? ...with no possibility of an air leak?
How about the battery voltage? ...when idling? ...and when attempting to rev?
Very significant information; "...airbox and filters are not installed..."
Strongly consider installing. Their absence would result to a massive air leak causing a very lean mix. The engine is starving for fuel but getting too much air. This would explain if not contribute largely to the hesitancy and the seeming flatspot @ 4500 RPMs.
Of course, it is still possible to have uneven quantity of fuel inside the carb bowls and/or the needles are not rising adeuqately. But yes, let's start with the air box and filter.
...and thank you for your kind understanding of automated-systems / machine-generated followups, ads & offers.