engine clapping sound

hello everyone, first time in the Forum and first time owning a motorcycle, just got a 1978 Kawasaki kz 650, got the carburetors rebuilt a few days ago..but now i can hear a clapping sound from the engine when is on an stalled right away..help please.

I would expect with that noise, a shim slipped out..... However, I think the 78 650 has under bucket shims.
RegardZ.