Need more details.
What is the history of the symptom?
Did it start happening all of a sudden? - like after removing the carbs?
Slowly get worse?
What's the engine mileage?
How long has the bike been sitting?
Leaking intake manifolds - constantly R&R the carbs will cause a leak.
Spray WD40 around the manifolds as the engine is racing - if the revs
change, you found a leak.
The WD40 will temporarily plug any leaks.
One or more chokes stuck open.
Carbs out of sync - with the carbs off, check that all 4 butterfly valves
are adjusted equally.
Lift the throttle slides with your fingers and let them drop - they should all
drop to the bottom at the same time.