It could be the carburetor, or the tube that connects it to the engine, or even the petcock.
Most modern carbs have synthetic rubber diaphragms that can tear, allowing excess air through. If you have a vacuum-operated petcock, the tube that connects it to the carb could be going bad, or the diaphragm in the petcock could fail.
Assuming you have done no carb work recently, it is unlikely that the carb has come unseated from the induction tube, but the tube could have cracked, or the seal between it and the head failed, possibly because the bolts/nuts that hold it on have loosened.
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'68-7? CB450 and '98 Valkyrie Tourer, too